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 $195.87   6.217%   $208.0472   $208.05   $208.05   $208.00  
  Purchase #2 $123.70   5.149%   $130.0693   $130.07   $130.05   $130.10  
  Purchase #3 $110.30   13.482%   $125.1706   $125.17   $125.15   $125.20  
  Purchase #4 $59.54   11.151%   $66.1793   $66.18   $66.20   $66.20  
  Purchase #5 $246.60   7.464%   $265.0062   $265.01   $265.00   $265.00  
  Purchase #6 $59.83   9.423%   $65.4678   $65.47   $65.45   $65.50  
  Purchase #7 $194.79   5.591%   $205.6807   $205.68   $205.70   $205.70  
  7 purchase totals = $990.63       $1,065.6211   $1,065.63   $1,065.60   $1,065.70