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 $65.86   11.567%   $73.478   $73.48   $73.50   $73.50  
  Purchase #2 $226.58   11.777%   $253.2643   $253.26   $253.25   $253.30  
  Purchase #3 $238.85   7.255%   $256.1786   $256.18   $256.20   $256.20  
  Purchase #4 $175.85   12.763%   $198.2937   $198.29   $198.30   $198.30  
  Purchase #5 $88.90   10.803%   $98.5039   $98.50   $98.50   $98.50  
  Purchase #6 $120.51   3.810%   $125.1014   $125.10   $125.10   $125.10  
  Purchase #7 $114.74   8.477%   $124.4665   $124.47   $124.45   $124.50  
  7 purchase totals = $1,031.29       $1,129.2864   $1,129.28   $1,129.30   $1,129.40