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 $234.47   12.428%   $263.6099   $263.61   $263.60   $263.60  
  Purchase #2 $96.58   9.114%   $105.3823   $105.38   $105.40   $105.40  
  Purchase #3 $71.39   3.431%   $73.8394   $73.84   $73.85   $73.80  
  Purchase #4 $93.47   9.457%   $102.3095   $102.31   $102.30   $102.30  
  Purchase #5 $8.39   8.163%   $9.0749   $9.07   $9.05   $9.10  
  Purchase #6 $10.40   4.317%   $10.849   $10.85   $10.85   $10.80  
  Purchase #7 $148.81   12.748%   $167.7803   $167.78   $167.80   $167.80  
  7 purchase totals = $663.51       $732.8453   $732.84   $732.85   $732.80