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 $47.39   4.627%   $49.5827   $49.58   $49.60   $49.60  
  Purchase #2 $126.55   5.658%   $133.7102   $133.71   $133.70   $133.70  
  Purchase #3 $247.49   10.280%   $272.932   $272.93   $272.95   $272.90  
  Purchase #4 $199.48   5.391%   $210.234   $210.23   $210.25   $210.20  
  Purchase #5 $131.36   12.284%   $147.4963   $147.50   $147.50   $147.50  
  Purchase #6 $242.73   6.521%   $258.5584   $258.56   $258.55   $258.60  
  Purchase #7 $188.25   11.185%   $209.3058   $209.31   $209.30   $209.30  
  7 purchase totals = $1,183.25       $1,281.8194   $1,281.82   $1,281.85   $1,281.80