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 $168.30   7.350%   $180.6701   $180.67   $180.65   $180.70  
  Purchase #2 $32.45   8.389%   $35.1722   $35.17   $35.15   $35.20  
  Purchase #3 $70.47   12.831%   $79.512   $79.51   $79.50   $79.50  
  Purchase #4 $86.35   12.239%   $96.9184   $96.92   $96.90   $96.90  
  Purchase #5 $174.59   10.464%   $192.8591   $192.86   $192.85   $192.90  
  Purchase #6 $196.62   3.571%   $203.6413   $203.64   $203.65   $203.60  
  Purchase #7 $213.97   10.119%   $235.6216   $235.62   $235.60   $235.60  
  7 purchase totals = $942.75       $1,024.3947   $1,024.39   $1,024.30   $1,024.40