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 $41.84   5.653%   $44.2052   $44.21   $44.20   $44.20  
  Purchase #2 $247.74   4.144%   $258.0063   $258.01   $258.00   $258.00  
  Purchase #3 $227.97   7.687%   $245.4941   $245.49   $245.50   $245.50  
  Purchase #4 $183.95   12.404%   $206.7672   $206.77   $206.75   $206.80  
  Purchase #5 $154.30   4.564%   $161.3423   $161.34   $161.35   $161.30  
  Purchase #6 $166.43   3.264%   $171.8623   $171.86   $171.85   $171.90  
  Purchase #7 $215.72   12.339%   $242.3377   $242.34   $242.35   $242.30  
  7 purchase totals = $1,237.95       $1,330.0151   $1,330.02   $1,330.00   $1,330.00