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 $53.45   5.202%   $56.2305   $56.23   $56.25   $56.20  
  Purchase #2 $117.29   7.140%   $125.6645   $125.66   $125.65   $125.70  
  Purchase #3 $109.72   13.693%   $124.744   $124.74   $124.75   $124.70  
  Purchase #4 $230.35   4.667%   $241.1004   $241.10   $241.10   $241.10  
  Purchase #5 $50.42   3.449%   $52.159   $52.16   $52.15   $52.20  
  Purchase #6 $230.66   8.400%   $250.0354   $250.04   $250.05   $250.00  
  Purchase #7 $92.33   4.846%   $96.8043   $96.80   $96.80   $96.80  
  7 purchase totals = $884.22       $946.7381   $946.73   $946.75   $946.70