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 $75.98   8.353%   $82.3266   $82.33   $82.35   $82.30  
  Purchase #2 $22.86   10.795%   $25.3277   $25.33   $25.35   $25.30  
  Purchase #3 $25.96   3.266%   $26.8079   $26.81   $26.80   $26.80  
  Purchase #4 $52.88   8.336%   $57.2881   $57.29   $57.30   $57.30  
  Purchase #5 $203.67   4.409%   $212.6498   $212.65   $212.65   $212.60  
  Purchase #6 $209.75   10.762%   $232.3233   $232.32   $232.30   $232.30  
  Purchase #7 $114.94   10.177%   $126.6374   $126.64   $126.65   $126.60  
  7 purchase totals = $706.04       $763.3608   $763.37   $763.40   $763.20