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 $58.86   3.816%   $61.1061   $61.11   $61.10   $61.10  
  Purchase #2 $47.84   7.607%   $51.4792   $51.48   $51.50   $51.50  
  Purchase #3 $135.27   8.206%   $146.3703   $146.37   $146.35   $146.40  
  Purchase #4 $41.93   4.844%   $43.9611   $43.96   $43.95   $44.00  
  Purchase #5 $232.69   5.282%   $244.9807   $244.98   $245.00   $245.00  
  Purchase #6 $236.31   8.350%   $256.0419   $256.04   $256.05   $256.00  
  Purchase #7 $170.93   6.589%   $182.1926   $182.19   $182.20   $182.20  
  7 purchase totals = $923.83       $986.1319   $986.13   $986.15   $986.20