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 $205.87   12.695%   $232.0052   $232.01   $232.00   $232.00  
  Purchase #2 $17.72   10.562%   $19.5916   $19.59   $19.60   $19.60  
  Purchase #3 $130.58   8.278%   $141.3894   $141.39   $141.40   $141.40  
  Purchase #4 $185.48   3.606%   $192.1684   $192.17   $192.15   $192.20  
  Purchase #5 $162.92   6.360%   $173.2817   $173.28   $173.30   $173.30  
  Purchase #6 $236.40   8.507%   $256.5105   $256.51   $256.50   $256.50  
  Purchase #7 $246.44   6.109%   $261.495   $261.50   $261.50   $261.50  
  7 purchase totals = $1,185.41       $1,276.4418   $1,276.45   $1,276.45   $1,276.50