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 $154.55   12.697%   $174.1732   $174.17   $174.15   $174.20  
  Purchase #2 $78.62   10.247%   $86.6762   $86.68   $86.70   $86.70  
  Purchase #3 $216.57   3.512%   $224.1759   $224.18   $224.20   $224.20  
  Purchase #4 $126.32   7.696%   $136.0416   $136.04   $136.05   $136.00  
  Purchase #5 $28.87   12.716%   $32.5411   $32.54   $32.55   $32.50  
  Purchase #6 $68.59   4.830%   $71.9029   $71.90   $71.90   $71.90  
  Purchase #7 $247.47   12.794%   $279.1313   $279.13   $279.15   $279.10  
  7 purchase totals = $920.99       $1,004.6422   $1,004.64   $1,004.70   $1,004.60