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 $241.51   8.872%   $262.9368   $262.94   $262.95   $262.90  
  Purchase #2 $56.94   7.311%   $61.1029   $61.10   $61.10   $61.10  
  Purchase #3 $17.62   11.350%   $19.6199   $19.62   $19.60   $19.60  
  Purchase #4 $170.98   13.611%   $194.2521   $194.25   $194.25   $194.30  
  Purchase #5 $47.98   11.153%   $53.3312   $53.33   $53.35   $53.30  
  Purchase #6 $61.49   9.761%   $67.492   $67.49   $67.50   $67.50  
  Purchase #7 $11.80   11.853%   $13.1987   $13.20   $13.20   $13.20  
  7 purchase totals = $608.32       $671.9336   $671.93   $671.95   $671.90