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 $185.43   10.527%   $204.9502   $204.95   $204.95   $205.00  
  Purchase #2 $66.33   5.133%   $69.7347   $69.73   $69.75   $69.70  
  Purchase #3 $226.72   4.117%   $236.0541   $236.05   $236.05   $236.10  
  Purchase #4 $237.67   3.149%   $245.1542   $245.15   $245.15   $245.20  
  Purchase #5 $234.63   6.672%   $250.2845   $250.28   $250.30   $250.30  
  Purchase #6 $45.89   13.735%   $52.193   $52.19   $52.20   $52.20  
  Purchase #7 $53.41   9.141%   $58.2922   $58.29   $58.30   $58.30  
  7 purchase totals = $1,050.08       $1,116.6629   $1,116.64   $1,116.70   $1,116.80