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 $60.87   12.719%   $68.6121   $68.61   $68.60   $68.60  
  Purchase #2 $217.51   4.803%   $227.957   $227.96   $227.95   $228.00  
  Purchase #3 $212.58   12.233%   $238.5849   $238.58   $238.60   $238.60  
  Purchase #4 $155.73   11.630%   $173.8414   $173.84   $173.85   $173.80  
  Purchase #5 $244.61   9.743%   $268.4424   $268.44   $268.45   $268.40  
  Purchase #6 $67.63   12.551%   $76.1182   $76.12   $76.10   $76.10  
  Purchase #7 $189.78   10.324%   $209.3729   $209.37   $209.35   $209.40  
  7 purchase totals = $1,148.71       $1,262.9289   $1,262.92   $1,262.90   $1,262.90