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 $199.76   9.624%   $218.9849   $218.98   $219.00   $219.00  
  Purchase #2 $9.62   9.423%   $10.5265   $10.53   $10.55   $10.50  
  Purchase #3 $125.65   5.664%   $132.7668   $132.77   $132.75   $132.80  
  Purchase #4 $229.30   7.225%   $245.8669   $245.87   $245.85   $245.90  
  Purchase #5 $84.66   7.273%   $90.8173   $90.82   $90.80   $90.80  
  Purchase #6 $193.86   8.747%   $210.8169   $210.82   $210.80   $210.80  
  Purchase #7 $120.94   4.139%   $125.9457   $125.95   $125.95   $125.90  
  7 purchase totals = $963.79       $1,035.7250   $1,035.74   $1,035.70   $1,035.70