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 $101.92   12.200%   $114.3542   $114.35   $114.35   $114.40  
  Purchase #2 $247.69   11.203%   $275.4387   $275.44   $275.45   $275.40  
  Purchase #3 $134.56   4.663%   $140.8345   $140.83   $140.85   $140.80  
  Purchase #4 $229.73   12.431%   $258.2877   $258.29   $258.30   $258.30  
  Purchase #5 $92.26   5.414%   $97.255   $97.26   $97.25   $97.30  
  Purchase #6 $137.36   5.182%   $144.478   $144.48   $144.50   $144.50  
  Purchase #7 $107.61   8.172%   $116.4039   $116.40   $116.40   $116.40  
  7 purchase totals = $1,051.13       $1,147.0520   $1,147.05   $1,147.10   $1,147.10