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 $60.45   8.801%   $65.7702   $65.77   $65.75   $65.80  
  Purchase #2 $187.44   12.248%   $210.3977   $210.40   $210.40   $210.40  
  Purchase #3 $215.41   6.443%   $229.2889   $229.29   $229.30   $229.30  
  Purchase #4 $198.32   13.232%   $224.5617   $224.56   $224.55   $224.60  
  Purchase #5 $45.92   3.845%   $47.6856   $47.69   $47.70   $47.70  
  Purchase #6 $29.97   13.430%   $33.995   $34.00   $34.00   $34.00  
  Purchase #7 $216.61   12.730%   $244.1845   $244.18   $244.20   $244.20  
  7 purchase totals = $954.12       $1,055.8836   $1,055.89   $1,055.90   $1,056.00