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 $28.83   13.127%   $32.6145   $32.61   $32.60   $32.60  
  Purchase #2 $178.42   9.188%   $194.8132   $194.81   $194.80   $194.80  
  Purchase #3 $78.60   7.791%   $84.7237   $84.72   $84.70   $84.70  
  Purchase #4 $125.97   10.149%   $138.7547   $138.75   $138.75   $138.80  
  Purchase #5 $66.73   3.187%   $68.8567   $68.86   $68.85   $68.90  
  Purchase #6 $244.57   5.127%   $257.1091   $257.11   $257.10   $257.10  
  Purchase #7 $177.29   5.243%   $186.5853   $186.59   $186.60   $186.60  
  7 purchase totals = $900.41       $963.4572   $963.45   $963.40   $963.50