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 $62.77   9.172%   $68.5273   $68.53   $68.55   $68.50  
  Purchase #2 $97.64   13.283%   $110.6095   $110.61   $110.60   $110.60  
  Purchase #3 $45.49   13.481%   $51.6225   $51.62   $51.60   $51.60  
  Purchase #4 $26.94   12.772%   $30.3808   $30.38   $30.40   $30.40  
  Purchase #5 $244.73   13.796%   $278.493   $278.49   $278.50   $278.50  
  Purchase #6 $44.80   6.422%   $47.6771   $47.68   $47.70   $47.70  
  Purchase #7 $222.79   11.375%   $248.1324   $248.13   $248.15   $248.10  
  7 purchase totals = $745.16       $835.4426   $835.44   $835.50   $835.40