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 $88.63   13.326%   $100.4408   $100.44   $100.45   $100.40  
  Purchase #2 $224.80   12.842%   $253.6688   $253.67   $253.65   $253.70  
  Purchase #3 $47.96   12.583%   $53.9948   $53.99   $54.00   $54.00  
  Purchase #4 $205.85   13.543%   $233.7283   $233.73   $233.75   $233.70  
  Purchase #5 $130.25   8.175%   $140.8979   $140.90   $140.90   $140.90  
  Purchase #6 $24.42   3.703%   $25.3243   $25.32   $25.30   $25.30  
  Purchase #7 $226.37   4.688%   $236.9822   $236.98   $237.00   $237.00  
  7 purchase totals = $948.28       $1,045.0371   $1,045.03   $1,045.05   $1,045.00