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 $135.34   12.250%   $151.9192   $151.92   $151.90   $151.90  
  Purchase #2 $244.29   6.420%   $259.9734   $259.97   $259.95   $260.00  
  Purchase #3 $37.78   7.358%   $40.5599   $40.56   $40.55   $40.60  
  Purchase #4 $214.86   9.685%   $235.6692   $235.67   $235.65   $235.70  
  Purchase #5 $55.44   9.842%   $60.8964   $60.90   $60.90   $60.90  
  Purchase #6 $52.58   7.505%   $56.5261   $56.53   $56.55   $56.50  
  Purchase #7 $213.78   3.795%   $221.893   $221.89   $221.90   $221.90  
  7 purchase totals = $954.07       $1,027.4372   $1,027.44   $1,027.40   $1,027.50