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 $63.95   10.256%   $70.5087   $70.51   $70.50   $70.50  
  Purchase #2 $220.42   6.392%   $234.5092   $234.51   $234.50   $234.50  
  Purchase #3 $217.77   4.764%   $228.1446   $228.14   $228.15   $228.10  
  Purchase #4 $236.51   6.133%   $251.0152   $251.02   $251.00   $251.00  
  Purchase #5 $58.80   8.790%   $63.9685   $63.97   $63.95   $64.00  
  Purchase #6 $115.41   3.114%   $119.0039   $119.00   $119.00   $119.00  
  Purchase #7 $9.30   11.453%   $10.3651   $10.37   $10.35   $10.40  
  7 purchase totals = $922.16       $977.5152   $977.52   $977.45   $977.50