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 $191.89   4.476%   $200.479   $200.48   $200.50   $200.50  
  Purchase #2 $61.79   13.321%   $70.021   $70.02   $70.00   $70.00  
  Purchase #3 $250.63   5.288%   $263.8833   $263.88   $263.90   $263.90  
  Purchase #4 $175.71   13.355%   $199.1761   $199.18   $199.20   $199.20  
  Purchase #5 $178.78   5.783%   $189.1188   $189.12   $189.10   $189.10  
  Purchase #6 $195.95   8.578%   $212.7586   $212.76   $212.75   $212.80  
  Purchase #7 $151.97   10.277%   $167.588   $167.59   $167.60   $167.60  
  7 purchase totals = $1,206.72       $1,303.0248   $1,303.03   $1,303.05   $1,303.10