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 $136.26   12.631%   $153.471   $153.47   $153.45   $153.50  
  Purchase #2 $185.63   7.205%   $199.0046   $199.00   $199.00   $199.00  
  Purchase #3 $25.36   12.797%   $28.6053   $28.61   $28.60   $28.60  
  Purchase #4 $115.34   8.670%   $125.34   $125.34   $125.35   $125.30  
  Purchase #5 $246.52   5.576%   $260.266   $260.27   $260.25   $260.30  
  Purchase #6 $21.99   13.168%   $24.8856   $24.89   $24.90   $24.90  
  Purchase #7 $249.84   11.109%   $277.5947   $277.59   $277.60   $277.60  
  7 purchase totals = $980.94       $1,069.1672   $1,069.17   $1,069.15   $1,069.20