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 $236.75   12.320%   $265.9176   $265.92   $265.90   $265.90  
  Purchase #2 $214.78   5.782%   $227.1986   $227.20   $227.20   $227.20  
  Purchase #3 $151.76   3.812%   $157.5451   $157.55   $157.55   $157.50  
  Purchase #4 $240.51   9.471%   $263.2887   $263.29   $263.30   $263.30  
  Purchase #5 $183.66   10.842%   $203.5724   $203.57   $203.55   $203.60  
  Purchase #6 $67.60   10.486%   $74.6885   $74.69   $74.70   $74.70  
  Purchase #7 $164.29   5.800%   $173.8188   $173.82   $173.80   $173.80  
  7 purchase totals = $1,259.35       $1,366.0297   $1,366.04   $1,366.00   $1,366.00