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 $119.51   10.771%   $132.3824   $132.38   $132.40   $132.40  
  Purchase #2 $140.47   8.294%   $152.1206   $152.12   $152.10   $152.10  
  Purchase #3 $218.66   5.307%   $230.2643   $230.26   $230.25   $230.30  
  Purchase #4 $190.38   12.565%   $214.3012   $214.30   $214.30   $214.30  
  Purchase #5 $95.81   8.515%   $103.9682   $103.97   $103.95   $104.00  
  Purchase #6 $13.44   10.329%   $14.8282   $14.83   $14.85   $14.80  
  Purchase #7 $157.49   5.874%   $166.741   $166.74   $166.75   $166.70  
  7 purchase totals = $935.76       $1,014.6059   $1,014.60   $1,014.60   $1,014.60