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 $36.66   10.106%   $40.3649   $40.36   $40.35   $40.40  
  Purchase #2 $168.51   3.289%   $174.0523   $174.05   $174.05   $174.10  
  Purchase #3 $103.25   11.121%   $114.7324   $114.73   $114.75   $114.70  
  Purchase #4 $174.63   9.871%   $191.8677   $191.87   $191.85   $191.90  
  Purchase #5 $56.38   13.627%   $64.0629   $64.06   $64.05   $64.10  
  Purchase #6 $234.56   11.702%   $262.0082   $262.01   $262.00   $262.00  
  Purchase #7 $99.39   4.265%   $103.629   $103.63   $103.65   $103.60  
  7 purchase totals = $873.38       $950.7174   $950.71   $950.70   $950.80