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 $216.28   13.613%   $245.7222   $245.72   $245.70   $245.70  
  Purchase #2 $17.97   4.218%   $18.728   $18.73   $18.75   $18.70  
  Purchase #3 $58.38   7.693%   $62.8712   $62.87   $62.85   $62.90  
  Purchase #4 $65.86   12.180%   $73.8817   $73.88   $73.90   $73.90  
  Purchase #5 $8.56   12.577%   $9.6366   $9.64   $9.65   $9.60  
  Purchase #6 $245.34   13.583%   $278.6645   $278.66   $278.65   $278.70  
  Purchase #7 $51.26   13.496%   $58.178   $58.18   $58.20   $58.20  
  7 purchase totals = $663.65       $747.6822   $747.68   $747.70   $747.70