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 $85.74   10.156%   $94.4478   $94.45   $94.45   $94.40  
  Purchase #2 $193.92   4.600%   $202.8403   $202.84   $202.85   $202.80  
  Purchase #3 $87.25   3.434%   $90.2462   $90.25   $90.25   $90.20  
  Purchase #4 $148.54   6.473%   $158.155   $158.16   $158.15   $158.20  
  Purchase #5 $15.62   4.671%   $16.3496   $16.35   $16.35   $16.30  
  Purchase #6 $34.67   6.386%   $36.884   $36.88   $36.90   $36.90  
  Purchase #7 $137.66   3.301%   $142.2042   $142.20   $142.20   $142.20  
  7 purchase totals = $703.40       $741.1271   $741.13   $741.15   $741.00