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 $64.67   13.382%   $73.3241   $73.32   $73.30   $73.30  
  Purchase #2 $89.86   3.679%   $93.1659   $93.17   $93.15   $93.20  
  Purchase #3 $65.38   4.740%   $68.479   $68.48   $68.50   $68.50  
  Purchase #4 $56.77   12.572%   $63.9071   $63.91   $63.90   $63.90  
  Purchase #5 $237.41   10.637%   $262.6633   $262.66   $262.65   $262.70  
  Purchase #6 $172.48   5.832%   $182.539   $182.54   $182.55   $182.50  
  Purchase #7 $148.38   5.208%   $156.1076   $156.11   $156.10   $156.10  
  7 purchase totals = $834.95       $900.1860   $900.19   $900.15   $900.20