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 $34.43   6.525%   $36.6766   $36.68   $36.70   $36.70  
  Purchase #2 $177.68   10.269%   $195.926   $195.93   $195.95   $195.90  
  Purchase #3 $250.68   11.716%   $280.0497   $280.05   $280.05   $280.00  
  Purchase #4 $86.58   5.228%   $91.1064   $91.11   $91.10   $91.10  
  Purchase #5 $233.80   10.410%   $258.1386   $258.14   $258.15   $258.10  
  Purchase #6 $195.56   13.226%   $221.4248   $221.42   $221.40   $221.40  
  Purchase #7 $59.95   9.689%   $65.7586   $65.76   $65.75   $65.80  
  7 purchase totals = $1,038.68       $1,149.0807   $1,149.09   $1,149.10   $1,149.00