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 $245.98   8.153%   $266.0347   $266.03   $266.05   $266.00  
  Purchase #2 $156.84   9.572%   $171.8527   $171.85   $171.85   $171.90  
  Purchase #3 $11.84   5.518%   $12.4933   $12.49   $12.50   $12.50  
  Purchase #4 $234.28   6.617%   $249.7823   $249.78   $249.80   $249.80  
  Purchase #5 $106.28   3.411%   $109.9052   $109.91   $109.90   $109.90  
  Purchase #6 $208.95   4.300%   $217.9349   $217.93   $217.95   $217.90  
  Purchase #7 $100.96   8.622%   $109.6648   $109.66   $109.65   $109.70  
  7 purchase totals = $1,065.13       $1,137.6679   $1,137.65   $1,137.70   $1,137.70