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 $29.48   9.779%   $32.3628   $32.36   $32.35   $32.40  
  Purchase #2 $84.82   13.678%   $96.4217   $96.42   $96.40   $96.40  
  Purchase #3 $240.37   13.495%   $272.8079   $272.81   $272.80   $272.80  
  Purchase #4 $42.91   8.125%   $46.3964   $46.40   $46.40   $46.40  
  Purchase #5 $167.84   7.183%   $179.8959   $179.90   $179.90   $179.90  
  Purchase #6 $182.91   10.614%   $202.3241   $202.32   $202.30   $202.30  
  Purchase #7 $57.35   11.782%   $64.107   $64.11   $64.10   $64.10  
  7 purchase totals = $805.68       $894.3158   $894.32   $894.25   $894.30