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 $54.69   13.579%   $62.1164   $62.12   $62.10   $62.10  
  Purchase #2 $227.53   9.320%   $248.7358   $248.74   $248.75   $248.70  
  Purchase #3 $22.45   13.664%   $25.5176   $25.52   $25.50   $25.50  
  Purchase #4 $98.66   3.348%   $101.9631   $101.96   $101.95   $102.00  
  Purchase #5 $96.38   12.379%   $108.3109   $108.31   $108.30   $108.30  
  Purchase #6 $195.81   6.747%   $209.0213   $209.02   $209.00   $209.00  
  Purchase #7 $154.47   10.678%   $170.9643   $170.96   $170.95   $171.00  
  7 purchase totals = $849.99       $926.6294   $926.63   $926.55   $926.60