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 $82.67   12.870%   $93.3096   $93.31   $93.30   $93.30  
  Purchase #2 $88.74   7.394%   $95.3014   $95.30   $95.30   $95.30  
  Purchase #3 $122.44   4.119%   $127.4833   $127.48   $127.50   $127.50  
  Purchase #4 $178.48   13.166%   $201.9787   $201.98   $202.00   $202.00  
  Purchase #5 $86.74   13.224%   $98.2105   $98.21   $98.20   $98.20  
  Purchase #6 $212.25   5.407%   $223.7264   $223.73   $223.75   $223.70  
  Purchase #7 $85.81   7.610%   $92.3401   $92.34   $92.35   $92.30  
  7 purchase totals = $857.13       $932.3500   $932.35   $932.40   $932.30