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 $66.38   10.776%   $73.5331   $73.53   $73.55   $73.50  
  Purchase #2 $203.77   8.554%   $221.2005   $221.20   $221.20   $221.20  
  Purchase #3 $238.40   10.259%   $262.8575   $262.86   $262.85   $262.90  
  Purchase #4 $213.87   6.302%   $227.3481   $227.35   $227.35   $227.30  
  Purchase #5 $160.89   10.615%   $177.9685   $177.97   $177.95   $178.00  
  Purchase #6 $9.60   13.410%   $10.8874   $10.89   $10.90   $10.90  
  Purchase #7 $246.74   11.721%   $275.6604   $275.66   $275.65   $275.70  
  7 purchase totals = $1,139.65       $1,249.4555   $1,249.46   $1,249.45   $1,249.50