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 $42.84   13.495%   $48.6213   $48.62   $48.60   $48.60  
  Purchase #2 $154.75   3.342%   $159.9217   $159.92   $159.90   $159.90  
  Purchase #3 $150.46   11.245%   $167.3792   $167.38   $167.40   $167.40  
  Purchase #4 $8.65   4.869%   $9.0712   $9.07   $9.05   $9.10  
  Purchase #5 $186.83   12.642%   $210.449   $210.45   $210.45   $210.40  
  Purchase #6 $48.53   4.255%   $50.595   $50.60   $50.60   $50.60  
  Purchase #7 $245.82   13.106%   $278.0372   $278.04   $278.05   $278.00  
  7 purchase totals = $837.88       $924.0746   $924.08   $924.05   $924.00