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 $125.39   8.748%   $136.3591   $136.36   $136.35   $136.40  
  Purchase #2 $130.46   8.622%   $141.7083   $141.71   $141.70   $141.70  
  Purchase #3 $186.27   7.352%   $199.9646   $199.96   $199.95   $200.00  
  Purchase #4 $192.65   5.619%   $203.475   $203.48   $203.50   $203.50  
  Purchase #5 $138.59   8.411%   $150.2468   $150.25   $150.25   $150.20  
  Purchase #6 $157.62   11.209%   $175.2876   $175.29   $175.30   $175.30  
  Purchase #7 $236.69   8.770%   $257.4477   $257.45   $257.45   $257.40  
  7 purchase totals = $1,167.67       $1,264.4891   $1,264.50   $1,264.50   $1,264.50