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 $205.64   9.815%   $225.8236   $225.82   $225.80   $225.80  
  Purchase #2 $29.96   11.802%   $33.4959   $33.50   $33.50   $33.50  
  Purchase #3 $224.26   13.351%   $254.201   $254.20   $254.20   $254.20  
  Purchase #4 $116.29   7.810%   $125.3722   $125.37   $125.35   $125.40  
  Purchase #5 $170.83   8.855%   $185.957   $185.96   $185.95   $186.00  
  Purchase #6 $46.48   7.567%   $49.9971   $50.00   $50.00   $50.00  
  Purchase #7 $237.51   7.614%   $255.594   $255.59   $255.60   $255.60  
  7 purchase totals = $1,030.97       $1,130.4408   $1,130.44   $1,130.40   $1,130.50