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 $151.83   3.801%   $157.6011   $157.60   $157.60   $157.60  
  Purchase #2 $26.30   3.218%   $27.1463   $27.15   $27.15   $27.10  
  Purchase #3 $174.43   11.265%   $194.0795   $194.08   $194.10   $194.10  
  Purchase #4 $86.44   13.361%   $97.9892   $97.99   $98.00   $98.00  
  Purchase #5 $153.67   10.496%   $169.7992   $169.80   $169.80   $169.80  
  Purchase #6 $209.51   13.385%   $237.5529   $237.55   $237.55   $237.60  
  Purchase #7 $83.71   10.408%   $92.4225   $92.42   $92.40   $92.40  
  7 purchase totals = $885.89       $976.5907   $976.59   $976.60   $976.60