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 $51.96   11.548%   $57.9603   $57.96   $57.95   $58.00  
  Purchase #2 $226.41   10.172%   $249.4404   $249.44   $249.45   $249.40  
  Purchase #3 $23.69   4.466%   $24.748   $24.75   $24.75   $24.70  
  Purchase #4 $90.29   7.147%   $96.743   $96.74   $96.75   $96.70  
  Purchase #5 $156.83   10.579%   $173.421   $173.42   $173.40   $173.40  
  Purchase #6 $49.65   4.247%   $51.7586   $51.76   $51.75   $51.80  
  Purchase #7 $74.75   9.425%   $81.7952   $81.80   $81.80   $81.80  
  7 purchase totals = $673.58       $735.8665   $735.87   $735.85   $735.80