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 $15.84   5.201%   $16.6638   $16.66   $16.65   $16.70  
  Purchase #2 $117.69   4.446%   $122.9225   $122.92   $122.90   $122.90  
  Purchase #3 $113.82   3.754%   $118.0928   $118.09   $118.10   $118.10  
  Purchase #4 $59.30   3.848%   $61.5819   $61.58   $61.60   $61.60  
  Purchase #5 $229.37   7.652%   $246.9214   $246.92   $246.90   $246.90  
  Purchase #6 $229.92   4.794%   $240.9424   $240.94   $240.95   $240.90  
  Purchase #7 $230.70   6.213%   $245.0334   $245.03   $245.05   $245.00  
  7 purchase totals = $996.64       $1,052.1582   $1,052.14   $1,052.15   $1,052.10