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 $68.53   9.731%   $75.1987   $75.20   $75.20   $75.20  
  Purchase #2 $226.97   12.337%   $254.9713   $254.97   $254.95   $255.00  
  Purchase #3 $105.78   12.802%   $119.322   $119.32   $119.30   $119.30  
  Purchase #4 $195.42   9.619%   $214.2174   $214.22   $214.20   $214.20  
  Purchase #5 $22.63   7.417%   $24.3085   $24.31   $24.30   $24.30  
  Purchase #6 $131.63   4.780%   $137.9219   $137.92   $137.90   $137.90  
  Purchase #7 $148.88   3.856%   $154.6208   $154.62   $154.60   $154.60  
  7 purchase totals = $899.84       $980.5606   $980.56   $980.45   $980.50