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 $119.43   12.840%   $134.7648   $134.76   $134.75   $134.80  
  Purchase #2 $67.30   8.551%   $73.0548   $73.05   $73.05   $73.10  
  Purchase #3 $234.27   10.557%   $259.0019   $259.00   $259.00   $259.00  
  Purchase #4 $245.74   8.791%   $267.343   $267.34   $267.35   $267.30  
  Purchase #5 $217.60   4.428%   $227.2353   $227.24   $227.25   $227.20  
  Purchase #6 $91.48   7.840%   $98.652   $98.65   $98.65   $98.70  
  Purchase #7 $240.44   9.379%   $262.9909   $262.99   $263.00   $263.00  
  7 purchase totals = $1,216.26       $1,323.0427   $1,323.03   $1,323.05   $1,323.10