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 $46.29   4.792%   $48.5082   $48.51   $48.50   $48.50  
  Purchase #2 $86.82   12.374%   $97.5631   $97.56   $97.55   $97.60  
  Purchase #3 $248.73   12.133%   $278.9084   $278.91   $278.90   $278.90  
  Purchase #4 $159.78   7.681%   $172.0527   $172.05   $172.05   $172.10  
  Purchase #5 $111.42   9.117%   $121.5782   $121.58   $121.60   $121.60  
  Purchase #6 $41.64   13.461%   $47.2452   $47.25   $47.25   $47.20  
  Purchase #7 $249.46   7.258%   $267.5658   $267.57   $267.55   $267.60  
  7 purchase totals = $944.14       $1,033.4216   $1,033.43   $1,033.40   $1,033.50