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 $61.61   3.232%   $63.6012   $63.60   $63.60   $63.60  
  Purchase #2 $210.65   6.674%   $224.7088   $224.71   $224.70   $224.70  
  Purchase #3 $30.91   12.266%   $34.7014   $34.70   $34.70   $34.70  
  Purchase #4 $105.94   5.503%   $111.7699   $111.77   $111.75   $111.80  
  Purchase #5 $120.37   13.389%   $136.4863   $136.49   $136.50   $136.50  
  Purchase #6 $169.80   6.586%   $180.983   $180.98   $181.00   $181.00  
  Purchase #7 $114.39   6.276%   $121.5691   $121.57   $121.55   $121.60  
  7 purchase totals = $813.67       $873.8197   $873.82   $873.80   $873.90