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 $245.91   11.141%   $273.3068   $273.31   $273.30   $273.30  
  Purchase #2 $111.83   11.375%   $124.5507   $124.55   $124.55   $124.60  
  Purchase #3 $188.48   3.539%   $195.1503   $195.15   $195.15   $195.20  
  Purchase #4 $196.95   7.116%   $210.965   $210.97   $210.95   $211.00  
  Purchase #5 $105.85   12.655%   $119.2453   $119.25   $119.25   $119.20  
  Purchase #6 $208.57   12.247%   $234.1136   $234.11   $234.10   $234.10  
  Purchase #7 $204.52   5.667%   $216.1101   $216.11   $216.10   $216.10  
  7 purchase totals = $1,262.11       $1,373.4418   $1,373.45   $1,373.40   $1,373.50