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 $32.29   6.254%   $34.3094   $34.31   $34.30   $34.30  
  Purchase #2 $154.59   6.266%   $164.2766   $164.28   $164.30   $164.30  
  Purchase #3 $85.71   10.792%   $94.9598   $94.96   $94.95   $95.00  
  Purchase #4 $132.70   4.701%   $138.9382   $138.94   $138.95   $138.90  
  Purchase #5 $88.34   4.659%   $92.4558   $92.46   $92.45   $92.50  
  Purchase #6 $238.97   10.464%   $263.9758   $263.98   $264.00   $264.00  
  Purchase #7 $63.55   5.443%   $67.009   $67.01   $67.00   $67.00  
  7 purchase totals = $796.15       $855.9246   $855.94   $855.95   $856.00