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 $84.87   11.158%   $94.3398   $94.34   $94.35   $94.30  
  Purchase #2 $93.98   6.447%   $100.0389   $100.04   $100.05   $100.00  
  Purchase #3 $155.86   7.689%   $167.8441   $167.84   $167.85   $167.80  
  Purchase #4 $76.95   10.489%   $85.0213   $85.02   $85.00   $85.00  
  Purchase #5 $180.80   11.865%   $202.2519   $202.25   $202.25   $202.30  
  Purchase #6 $66.38   11.667%   $74.1246   $74.12   $74.10   $74.10  
  Purchase #7 $208.34   12.264%   $233.8908   $233.89   $233.90   $233.90  
  7 purchase totals = $867.18       $957.5114   $957.50   $957.50   $957.40