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 $153.48   12.574%   $172.7786   $172.78   $172.80   $172.80  
  Purchase #2 $61.93   11.476%   $69.0371   $69.04   $69.05   $69.00  
  Purchase #3 $177.36   12.637%   $199.773   $199.77   $199.75   $199.80  
  Purchase #4 $95.42   8.472%   $103.504   $103.50   $103.50   $103.50  
  Purchase #5 $47.52   13.236%   $53.8097   $53.81   $53.80   $53.80  
  Purchase #6 $241.38   10.794%   $267.4346   $267.43   $267.45   $267.40  
  Purchase #7 $62.77   4.655%   $65.6919   $65.69   $65.70   $65.70  
  7 purchase totals = $839.86       $932.0289   $932.02   $932.05   $932.00