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 $82.53   7.311%   $88.5638   $88.56   $88.55   $88.60  
  Purchase #2 $243.69   6.800%   $260.2609   $260.26   $260.25   $260.30  
  Purchase #3 $44.52   5.116%   $46.7976   $46.80   $46.80   $46.80  
  Purchase #4 $241.70   10.870%   $267.9728   $267.97   $267.95   $268.00  
  Purchase #5 $128.28   13.508%   $145.6081   $145.61   $145.60   $145.60  
  Purchase #6 $202.82   3.501%   $209.9207   $209.92   $209.90   $209.90  
  Purchase #7 $137.62   7.665%   $148.1686   $148.17   $148.15   $148.20  
  7 purchase totals = $1,081.16       $1,167.2925   $1,167.29   $1,167.20   $1,167.40