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 $203.95   11.157%   $226.7047   $226.70   $226.70   $226.70  
  Purchase #2 $27.74   10.870%   $30.7553   $30.76   $30.75   $30.80  
  Purchase #3 $34.91   6.773%   $37.2745   $37.27   $37.25   $37.30  
  Purchase #4 $167.92   3.296%   $173.4546   $173.45   $173.45   $173.50  
  Purchase #5 $220.62   9.287%   $241.109   $241.11   $241.10   $241.10  
  Purchase #6 $104.80   4.175%   $109.1754   $109.18   $109.20   $109.20  
  Purchase #7 $92.54   10.146%   $101.9291   $101.93   $101.95   $101.90  
  7 purchase totals = $852.48       $920.4026   $920.40   $920.40   $920.50