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 $60.72   5.410%   $64.005   $64.01   $64.00   $64.00  
  Purchase #2 $109.26   6.457%   $116.3149   $116.31   $116.30   $116.30  
  Purchase #3 $54.52   8.179%   $58.9792   $58.98   $59.00   $59.00  
  Purchase #4 $44.68   7.409%   $47.9903   $47.99   $48.00   $48.00  
  Purchase #5 $140.85   5.864%   $149.1094   $149.11   $149.10   $149.10  
  Purchase #6 $127.33   11.539%   $142.0226   $142.02   $142.00   $142.00  
  Purchase #7 $235.98   3.370%   $243.9325   $243.93   $243.95   $243.90  
  7 purchase totals = $773.34       $822.3539   $822.35   $822.35   $822.30