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 $61.54   8.173%   $66.5697   $66.57   $66.55   $66.60  
  Purchase #2 $193.76   4.349%   $202.1866   $202.19   $202.20   $202.20  
  Purchase #3 $147.82   7.155%   $158.3965   $158.40   $158.40   $158.40  
  Purchase #4 $116.97   11.292%   $130.1783   $130.18   $130.20   $130.20  
  Purchase #5 $78.54   6.849%   $83.9192   $83.92   $83.90   $83.90  
  Purchase #6 $17.25   6.829%   $18.428   $18.43   $18.45   $18.40  
  Purchase #7 $40.63   3.825%   $42.1841   $42.18   $42.20   $42.20  
  7 purchase totals = $656.51       $701.8624   $701.87   $701.90   $701.90