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 $207.33   12.114%   $232.446   $232.45   $232.45   $232.40  
  Purchase #2 $101.79   10.523%   $112.5014   $112.50   $112.50   $112.50  
  Purchase #3 $247.61   3.335%   $255.8678   $255.87   $255.85   $255.90  
  Purchase #4 $49.35   6.768%   $52.69   $52.69   $52.70   $52.70  
  Purchase #5 $53.34   13.797%   $60.6993   $60.70   $60.70   $60.70  
  Purchase #6 $10.99   12.849%   $12.4021   $12.40   $12.40   $12.40  
  Purchase #7 $5.62   11.183%   $6.2485   $6.25   $6.25   $6.20  
  7 purchase totals = $676.03       $732.8551   $732.86   $732.85   $732.80