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 $127.51   5.475%   $134.4912   $134.49   $134.50   $134.50  
  Purchase #2 $193.41   5.564%   $204.1713   $204.17   $204.15   $204.20  
  Purchase #3 $229.57   6.652%   $244.841   $244.84   $244.85   $244.80  
  Purchase #4 $205.78   12.597%   $231.7021   $231.70   $231.70   $231.70  
  Purchase #5 $96.90   9.340%   $105.9505   $105.95   $105.95   $106.00  
  Purchase #6 $59.87   8.345%   $64.8662   $64.87   $64.85   $64.90  
  Purchase #7 $209.94   4.165%   $218.684   $218.68   $218.70   $218.70  
  7 purchase totals = $1,122.98       $1,204.7063   $1,204.70   $1,204.70   $1,204.80