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 $169.79   3.669%   $176.0196   $176.02   $176.00   $176.00  
  Purchase #2 $224.40   9.140%   $244.9102   $244.91   $244.90   $244.90  
  Purchase #3 $27.29   5.207%   $28.711   $28.71   $28.70   $28.70  
  Purchase #4 $141.91   4.772%   $148.6819   $148.68   $148.70   $148.70  
  Purchase #5 $144.78   3.131%   $149.3131   $149.31   $149.30   $149.30  
  Purchase #6 $59.94   6.776%   $64.0015   $64.00   $64.00   $64.00  
  Purchase #7 $182.33   13.266%   $206.5179   $206.52   $206.50   $206.50  
  7 purchase totals = $950.44       $1,018.1552   $1,018.15   $1,018.10   $1,018.10