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 $71.85   6.478%   $76.5044   $76.50   $76.50   $76.50  
  Purchase #2 $121.46   10.117%   $133.7481   $133.75   $133.75   $133.70  
  Purchase #3 $153.98   13.246%   $174.3762   $174.38   $174.40   $174.40  
  Purchase #4 $37.85   11.385%   $42.1592   $42.16   $42.15   $42.20  
  Purchase #5 $217.41   7.821%   $234.4136   $234.41   $234.40   $234.40  
  Purchase #6 $100.35   13.826%   $114.2244   $114.22   $114.20   $114.20  
  Purchase #7 $205.95   9.737%   $226.0034   $226.00   $226.00   $226.00  
  7 purchase totals = $908.85       $1,001.4293   $1,001.42   $1,001.40   $1,001.40