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 $163.76   13.393%   $185.6924   $185.69   $185.70   $185.70  
  Purchase #2 $144.63   10.514%   $159.8364   $159.84   $159.85   $159.80  
  Purchase #3 $117.30   10.198%   $129.2623   $129.26   $129.25   $129.30  
  Purchase #4 $70.80   5.349%   $74.5871   $74.59   $74.60   $74.60  
  Purchase #5 $20.72   4.229%   $21.5962   $21.60   $21.60   $21.60  
  Purchase #6 $196.66   7.151%   $210.7232   $210.72   $210.70   $210.70  
  Purchase #7 $249.64   12.869%   $281.7662   $281.77   $281.75   $281.80  
  7 purchase totals = $963.51       $1,063.4638   $1,063.47   $1,063.45   $1,063.50