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 $52.38   10.690%   $57.9794   $57.98   $58.00   $58.00  
  Purchase #2 $44.78   3.692%   $46.4333   $46.43   $46.45   $46.40  
  Purchase #3 $11.35   3.736%   $11.774   $11.77   $11.75   $11.80  
  Purchase #4 $108.82   7.472%   $116.951   $116.95   $116.95   $117.00  
  Purchase #5 $117.71   11.283%   $130.9912   $130.99   $131.00   $131.00  
  Purchase #6 $121.52   9.472%   $133.0304   $133.03   $133.05   $133.00  
  Purchase #7 $249.25   6.226%   $264.7683   $264.77   $264.75   $264.80  
  7 purchase totals = $705.81       $761.9276   $761.92   $761.95   $762.00