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 $191.57   8.158%   $207.1983   $207.20   $207.20   $207.20  
  Purchase #2 $152.26   6.140%   $161.6088   $161.61   $161.60   $161.60  
  Purchase #3 $100.30   6.474%   $106.7934   $106.79   $106.80   $106.80  
  Purchase #4 $193.73   12.683%   $218.3008   $218.30   $218.30   $218.30  
  Purchase #5 $28.54   4.815%   $29.9142   $29.91   $29.90   $29.90  
  Purchase #6 $20.94   12.211%   $23.497   $23.50   $23.50   $23.50  
  Purchase #7 $227.54   9.653%   $249.5044   $249.50   $249.50   $249.50  
  7 purchase totals = $914.88       $996.8169   $996.81   $996.80   $996.80