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 $88.69   5.659%   $93.709   $93.71   $93.70   $93.70  
  Purchase #2 $249.57   10.823%   $276.581   $276.58   $276.60   $276.60  
  Purchase #3 $188.63   8.250%   $204.192   $204.19   $204.20   $204.20  
  Purchase #4 $231.61   12.201%   $259.8687   $259.87   $259.85   $259.90  
  Purchase #5 $104.67   8.610%   $113.6821   $113.68   $113.70   $113.70  
  Purchase #6 $234.31   11.519%   $261.3002   $261.30   $261.30   $261.30  
  Purchase #7 $23.92   4.413%   $24.9756   $24.98   $25.00   $25.00  
  7 purchase totals = $1,121.40       $1,234.3086   $1,234.31   $1,234.35   $1,234.40