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 $94.43   3.496%   $97.7313   $97.73   $97.75   $97.70  
  Purchase #2 $212.68   13.539%   $241.4747   $241.47   $241.45   $241.50  
  Purchase #3 $114.88   6.374%   $122.2025   $122.20   $122.20   $122.20  
  Purchase #4 $84.45   7.356%   $90.6621   $90.66   $90.65   $90.70  
  Purchase #5 $215.54   6.643%   $229.8583   $229.86   $229.85   $229.90  
  Purchase #6 $105.82   11.104%   $117.5703   $117.57   $117.55   $117.60  
  Purchase #7 $44.52   12.472%   $50.0725   $50.07   $50.05   $50.10  
  7 purchase totals = $872.32       $949.5717   $949.56   $949.50   $949.70