Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $172.95   12.282%   $194.1917   $194.19   $194.20   $194.20  
  Purchase #2 $199.78   11.262%   $222.2792   $222.28   $222.30   $222.30  
  Purchase #3 $161.50   5.108%   $169.7494   $169.75   $169.75   $169.70  
  Purchase #4 $135.87   11.692%   $151.7559   $151.76   $151.75   $151.80  
  Purchase #5 $118.52   13.625%   $134.6684   $134.67   $134.65   $134.70  
  Purchase #6 $246.59   11.270%   $274.3807   $274.38   $274.40   $274.40  
  Purchase #7 $125.96   7.796%   $135.7798   $135.78   $135.80   $135.80  
  7 purchase totals = $1,161.17       $1,282.8051   $1,282.81   $1,282.85   $1,282.90