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 $24.98   10.608%   $27.6299   $27.63   $27.65   $27.60  
  Purchase #2 $205.69   5.613%   $217.2354   $217.24   $217.25   $217.20  
  Purchase #3 $172.75   5.485%   $182.2253   $182.23   $182.25   $182.20  
  Purchase #4 $155.83   5.727%   $164.7544   $164.75   $164.75   $164.80  
  Purchase #5 $87.81   10.107%   $96.685   $96.69   $96.70   $96.70  
  Purchase #6 $124.51   11.693%   $139.069   $139.07   $139.05   $139.10  
  Purchase #7 $221.67   6.329%   $235.6995   $235.70   $235.70   $235.70  
  7 purchase totals = $993.24       $1,063.2985   $1,063.31   $1,063.35   $1,063.30