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 $196.85   7.210%   $211.0429   $211.04   $211.05   $211.00  
  Purchase #2 $82.73   4.395%   $86.366   $86.37   $86.35   $86.40  
  Purchase #3 $210.62   5.687%   $222.598   $222.60   $222.60   $222.60  
  Purchase #4 $25.92   3.794%   $26.9034   $26.90   $26.90   $26.90  
  Purchase #5 $211.88   10.852%   $234.8732   $234.87   $234.85   $234.90  
  Purchase #6 $45.84   11.188%   $50.9686   $50.97   $50.95   $51.00  
  Purchase #7 $105.57   4.521%   $110.3428   $110.34   $110.35   $110.30  
  7 purchase totals = $879.41       $943.0949   $943.09   $943.05   $943.10