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 $213.65   8.462%   $231.7291   $231.73   $231.75   $231.70  
  Purchase #2 $188.62   7.792%   $203.3173   $203.32   $203.30   $203.30  
  Purchase #3 $26.39   3.255%   $27.249   $27.25   $27.25   $27.20  
  Purchase #4 $78.36   10.472%   $86.5659   $86.57   $86.55   $86.60  
  Purchase #5 $227.92   7.205%   $244.3416   $244.34   $244.35   $244.30  
  Purchase #6 $209.89   11.376%   $233.7671   $233.77   $233.75   $233.80  
  Purchase #7 $132.41   5.734%   $140.0024   $140.00   $140.00   $140.00  
  7 purchase totals = $1,077.24       $1,166.9724   $1,166.98   $1,166.95   $1,166.90