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 $116.82   5.422%   $123.154   $123.15   $123.15   $123.20  
  Purchase #2 $43.32   3.761%   $44.9493   $44.95   $44.95   $44.90  
  Purchase #3 $108.68   5.251%   $114.3868   $114.39   $114.40   $114.40  
  Purchase #4 $139.38   9.795%   $153.0323   $153.03   $153.05   $153.00  
  Purchase #5 $40.27   10.725%   $44.589   $44.59   $44.60   $44.60  
  Purchase #6 $35.68   10.870%   $39.5584   $39.56   $39.55   $39.60  
  Purchase #7 $167.29   4.343%   $174.5554   $174.56   $174.55   $174.60  
  7 purchase totals = $651.44       $694.2252   $694.23   $694.25   $694.30