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 $183.73   12.187%   $206.1212   $206.12   $206.10   $206.10  
  Purchase #2 $208.79   12.236%   $234.3375   $234.34   $234.35   $234.30  
  Purchase #3 $59.74   12.316%   $67.0976   $67.10   $67.10   $67.10  
  Purchase #4 $75.57   9.243%   $82.5549   $82.55   $82.55   $82.60  
  Purchase #5 $125.99   12.172%   $141.3255   $141.33   $141.35   $141.30  
  Purchase #6 $241.43   5.218%   $254.0278   $254.03   $254.05   $254.00  
  Purchase #7 $242.38   7.759%   $261.1863   $261.19   $261.20   $261.20  
  7 purchase totals = $1,137.63       $1,246.6508   $1,246.66   $1,246.70   $1,246.60