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 $218.33   13.154%   $247.0491   $247.05   $247.05   $247.00  
  Purchase #2 $79.37   8.397%   $86.0347   $86.03   $86.05   $86.00  
  Purchase #3 $242.89   6.728%   $259.2316   $259.23   $259.25   $259.20  
  Purchase #4 $52.68   12.451%   $59.2392   $59.24   $59.25   $59.20  
  Purchase #5 $216.74   11.744%   $242.1939   $242.19   $242.20   $242.20  
  Purchase #6 $242.97   10.573%   $268.6592   $268.66   $268.65   $268.70  
  Purchase #7 $249.59   5.670%   $263.7418   $263.74   $263.75   $263.70  
  7 purchase totals = $1,302.57       $1,426.1495   $1,426.14   $1,426.20   $1,426.00