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 $93.72   4.758%   $98.1792   $98.18   $98.20   $98.20  
  Purchase #2 $216.63   7.676%   $233.2585   $233.26   $233.25   $233.30  
  Purchase #3 $31.43   13.372%   $35.6328   $35.63   $35.65   $35.60  
  Purchase #4 $238.27   4.726%   $249.5306   $249.53   $249.55   $249.50  
  Purchase #5 $83.28   6.324%   $88.5466   $88.55   $88.55   $88.50  
  Purchase #6 $180.45   6.660%   $192.468   $192.47   $192.45   $192.50  
  Purchase #7 $106.32   6.322%   $113.0416   $113.04   $113.05   $113.00  
  7 purchase totals = $950.10       $1,010.6573   $1,010.66   $1,010.70   $1,010.60