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 $85.95   8.812%   $93.5239   $93.52   $93.50   $93.50  
  Purchase #2 $101.80   5.359%   $107.2555   $107.26   $107.25   $107.30  
  Purchase #3 $108.93   6.856%   $116.3982   $116.40   $116.40   $116.40  
  Purchase #4 $193.91   13.842%   $220.751   $220.75   $220.75   $220.80  
  Purchase #5 $114.96   5.434%   $121.2069   $121.21   $121.20   $121.20  
  Purchase #6 $57.27   13.474%   $64.9866   $64.99   $65.00   $65.00  
  Purchase #7 $132.34   5.198%   $139.219   $139.22   $139.20   $139.20  
  7 purchase totals = $795.16       $863.3411   $863.35   $863.30   $863.40