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 $53.82   4.440%   $56.2096   $56.21   $56.20   $56.20  
  Purchase #2 $32.41   8.864%   $35.2828   $35.28   $35.30   $35.30  
  Purchase #3 $87.81   5.271%   $92.4385   $92.44   $92.45   $92.40  
  Purchase #4 $175.91   9.719%   $193.0067   $193.01   $193.00   $193.00  
  Purchase #5 $88.67   5.850%   $93.8572   $93.86   $93.85   $93.90  
  Purchase #6 $217.39   6.706%   $231.9682   $231.97   $231.95   $232.00  
  Purchase #7 $125.45   5.564%   $132.43   $132.43   $132.45   $132.40  
  7 purchase totals = $781.46       $835.1930   $835.20   $835.20   $835.20