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 $69.49   5.791%   $73.5142   $73.51   $73.50   $73.50  
  Purchase #2 $204.53   10.380%   $225.7602   $225.76   $225.75   $225.80  
  Purchase #3 $69.26   11.740%   $77.3911   $77.39   $77.40   $77.40  
  Purchase #4 $109.49   12.487%   $123.162   $123.16   $123.15   $123.20  
  Purchase #5 $169.38   13.637%   $192.4784   $192.48   $192.50   $192.50  
  Purchase #6 $191.92   5.138%   $201.7808   $201.78   $201.80   $201.80  
  Purchase #7 $59.56   3.327%   $61.5416   $61.54   $61.55   $61.50  
  7 purchase totals = $873.63       $955.6283   $955.62   $955.65   $955.70