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 $133.38   13.650%   $151.5864   $151.59   $151.60   $151.60  
  Purchase #2 $233.97   13.849%   $266.3725   $266.37   $266.35   $266.40  
  Purchase #3 $221.64   13.593%   $251.7675   $251.77   $251.75   $251.80  
  Purchase #4 $41.32   7.312%   $44.3413   $44.34   $44.35   $44.30  
  Purchase #5 $196.33   6.543%   $209.1759   $209.18   $209.20   $209.20  
  Purchase #6 $216.79   6.694%   $231.3019   $231.30   $231.30   $231.30  
  Purchase #7 $101.82   12.503%   $114.5506   $114.55   $114.55   $114.60  
  7 purchase totals = $1,145.25       $1,269.0961   $1,269.10   $1,269.10   $1,269.20