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 $162.74   13.431%   $184.5976   $184.60   $184.60   $184.60  
  Purchase #2 $164.47   13.313%   $186.3659   $186.37   $186.35   $186.40  
  Purchase #3 $152.64   13.256%   $172.874   $172.87   $172.85   $172.90  
  Purchase #4 $30.55   11.491%   $34.0605   $34.06   $34.05   $34.10  
  Purchase #5 $141.38   9.383%   $154.6457   $154.65   $154.65   $154.60  
  Purchase #6 $229.32   3.415%   $237.1513   $237.15   $237.15   $237.20  
  Purchase #7 $62.26   6.597%   $66.3673   $66.37   $66.35   $66.40  
  7 purchase totals = $943.36       $1,036.0623   $1,036.07   $1,036.00   $1,036.20