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 $196.98   8.455%   $213.6347   $213.63   $213.65   $213.60  
  Purchase #2 $125.85   7.158%   $134.8583   $134.86   $134.85   $134.90  
  Purchase #3 $60.84   11.361%   $67.752   $67.75   $67.75   $67.80  
  Purchase #4 $93.52   13.445%   $106.0938   $106.09   $106.10   $106.10  
  Purchase #5 $157.47   13.621%   $178.919   $178.92   $178.90   $178.90  
  Purchase #6 $147.63   7.117%   $158.1368   $158.14   $158.15   $158.10  
  Purchase #7 $229.69   10.376%   $253.5226   $253.52   $253.50   $253.50  
  7 purchase totals = $1,011.98       $1,112.9172   $1,112.91   $1,112.90   $1,112.90