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 $246.38   12.156%   $276.33   $276.33   $276.35   $276.30  
  Purchase #2 $190.34   12.351%   $213.8489   $213.85   $213.85   $213.80  
  Purchase #3 $68.47   3.450%   $70.8322   $70.83   $70.85   $70.80  
  Purchase #4 $53.53   5.783%   $56.6256   $56.63   $56.65   $56.60  
  Purchase #5 $197.74   11.575%   $220.6284   $220.63   $220.65   $220.60  
  Purchase #6 $248.27   4.838%   $260.2813   $260.28   $260.30   $260.30  
  Purchase #7 $83.32   11.125%   $92.5894   $92.59   $92.60   $92.60  
  7 purchase totals = $1,088.05       $1,191.1358   $1,191.14   $1,191.25   $1,191.00