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 $93.26   11.814%   $104.2777   $104.28   $104.30   $104.30  
  Purchase #2 $88.57   8.764%   $96.3323   $96.33   $96.35   $96.30  
  Purchase #3 $74.75   4.379%   $78.0233   $78.02   $78.00   $78.00  
  Purchase #4 $66.32   12.369%   $74.5231   $74.52   $74.50   $74.50  
  Purchase #5 $105.71   11.597%   $117.9692   $117.97   $117.95   $118.00  
  Purchase #6 $239.41   11.545%   $267.0499   $267.05   $267.05   $267.00  
  Purchase #7 $205.49   6.256%   $218.3455   $218.35   $218.35   $218.30  
  7 purchase totals = $873.51       $956.5210   $956.52   $956.50   $956.40