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 $239.61   5.806%   $253.5218   $253.52   $253.50   $253.50  
  Purchase #2 $125.86   9.182%   $137.4165   $137.42   $137.40   $137.40  
  Purchase #3 $123.32   4.404%   $128.751   $128.75   $128.75   $128.80  
  Purchase #4 $243.53   7.150%   $260.9424   $260.94   $260.95   $260.90  
  Purchase #5 $128.33   9.594%   $140.642   $140.64   $140.65   $140.60  
  Purchase #6 $167.32   3.366%   $172.952   $172.95   $172.95   $173.00  
  Purchase #7 $105.47   8.118%   $114.0321   $114.03   $114.05   $114.00  
  7 purchase totals = $1,133.44       $1,208.2578   $1,208.25   $1,208.25   $1,208.20