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 $59.41   3.569%   $61.5303   $61.53   $61.55   $61.50  
  Purchase #2 $24.92   9.212%   $27.2156   $27.22   $27.20   $27.20  
  Purchase #3 $194.39   10.117%   $214.0564   $214.06   $214.05   $214.10  
  Purchase #4 $168.99   8.464%   $183.2933   $183.29   $183.30   $183.30  
  Purchase #5 $41.90   9.215%   $45.7611   $45.76   $45.75   $45.80  
  Purchase #6 $9.58   5.360%   $10.0935   $10.09   $10.10   $10.10  
  Purchase #7 $157.82   6.811%   $168.5691   $168.57   $168.55   $168.60  
  7 purchase totals = $657.01       $710.5193   $710.52   $710.50   $710.60