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 $211.59   13.532%   $240.2224   $240.22   $240.20   $240.20  
  Purchase #2 $121.37   10.489%   $134.1005   $134.10   $134.10   $134.10  
  Purchase #3 $190.26   6.142%   $201.9458   $201.95   $201.95   $201.90  
  Purchase #4 $241.30   13.792%   $274.5801   $274.58   $274.60   $274.60  
  Purchase #5 $165.95   5.311%   $174.7636   $174.76   $174.75   $174.80  
  Purchase #6 $64.35   3.109%   $66.3506   $66.35   $66.35   $66.40  
  Purchase #7 $214.63   11.824%   $240.0079   $240.01   $240.00   $240.00  
  7 purchase totals = $1,209.45       $1,331.9709   $1,331.97   $1,331.95   $1,332.00