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 $111.59   6.131%   $118.4316   $118.43   $118.45   $118.40  
  Purchase #2 $239.66   9.602%   $262.6722   $262.67   $262.65   $262.70  
  Purchase #3 $187.34   12.364%   $210.5027   $210.50   $210.50   $210.50  
  Purchase #4 $31.66   8.447%   $34.3343   $34.33   $34.35   $34.30  
  Purchase #5 $43.99   6.152%   $46.6963   $46.70   $46.70   $46.70  
  Purchase #6 $250.68   13.665%   $284.9354   $284.94   $284.95   $284.90  
  Purchase #7 $110.86   13.282%   $125.5844   $125.58   $125.60   $125.60  
  7 purchase totals = $975.78       $1,083.1569   $1,083.15   $1,083.20   $1,083.10