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 $103.64   10.323%   $114.3388   $114.34   $114.35   $114.30  
  Purchase #2 $80.62   13.365%   $91.3949   $91.39   $91.40   $91.40  
  Purchase #3 $146.51   6.261%   $155.683   $155.68   $155.70   $155.70  
  Purchase #4 $241.94   6.771%   $258.3218   $258.32   $258.30   $258.30  
  Purchase #5 $207.89   12.306%   $233.4729   $233.47   $233.45   $233.50  
  Purchase #6 $81.42   12.232%   $91.3793   $91.38   $91.40   $91.40  
  Purchase #7 $87.37   6.159%   $92.7511   $92.75   $92.75   $92.80  
  7 purchase totals = $949.39       $1,037.3418   $1,037.33   $1,037.35   $1,037.40