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 $214.90   12.477%   $241.7131   $241.71   $241.70   $241.70  
  Purchase #2 $97.32   13.147%   $110.1147   $110.11   $110.10   $110.10  
  Purchase #3 $73.84   4.253%   $76.9804   $76.98   $77.00   $77.00  
  Purchase #4 $95.36   8.617%   $103.5772   $103.58   $103.60   $103.60  
  Purchase #5 $21.44   13.146%   $24.2585   $24.26   $24.25   $24.30  
  Purchase #6 $154.50   8.589%   $167.77   $167.77   $167.75   $167.80  
  Purchase #7 $82.96   13.497%   $94.1571   $94.16   $94.15   $94.20  
  7 purchase totals = $740.32       $818.5710   $818.57   $818.55   $818.70