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 $214.35   10.785%   $237.4676   $237.47   $237.45   $237.50  
  Purchase #2 $230.96   13.281%   $261.6338   $261.63   $261.65   $261.60  
  Purchase #3 $105.59   6.615%   $112.5748   $112.57   $112.55   $112.60  
  Purchase #4 $131.65   12.211%   $147.7258   $147.73   $147.75   $147.70  
  Purchase #5 $239.73   4.761%   $251.1435   $251.14   $251.15   $251.10  
  Purchase #6 $106.63   10.195%   $117.5009   $117.50   $117.50   $117.50  
  Purchase #7 $148.59   7.788%   $160.1622   $160.16   $160.15   $160.20  
  7 purchase totals = $1,177.50       $1,288.2086   $1,288.20   $1,288.20   $1,288.20