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 $47.39   13.611%   $53.8403   $53.84   $53.85   $53.80  
  Purchase #2 $115.45   8.376%   $125.1201   $125.12   $125.10   $125.10  
  Purchase #3 $206.92   3.363%   $213.8787   $213.88   $213.90   $213.90  
  Purchase #4 $60.25   10.155%   $66.3684   $66.37   $66.35   $66.40  
  Purchase #5 $79.45   7.327%   $85.2713   $85.27   $85.25   $85.30  
  Purchase #6 $247.94   9.494%   $271.4794   $271.48   $271.50   $271.50  
  Purchase #7 $33.75   8.425%   $36.5934   $36.59   $36.60   $36.60  
  7 purchase totals = $791.15       $852.5516   $852.55   $852.55   $852.60