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 $55.29   9.562%   $60.5768   $60.58   $60.60   $60.60  
  Purchase #2 $113.43   9.645%   $124.3703   $124.37   $124.35   $124.40  
  Purchase #3 $236.80   4.449%   $247.3352   $247.34   $247.35   $247.30  
  Purchase #4 $90.28   8.699%   $98.1335   $98.13   $98.15   $98.10  
  Purchase #5 $164.92   7.440%   $177.19   $177.19   $177.20   $177.20  
  Purchase #6 $192.47   9.348%   $210.4621   $210.46   $210.45   $210.50  
  Purchase #7 $101.49   12.699%   $114.3782   $114.38   $114.40   $114.40  
  7 purchase totals = $954.68       $1,032.4461   $1,032.45   $1,032.50   $1,032.50