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 $121.66   3.559%   $125.9899   $125.99   $126.00   $126.00  
  Purchase #2 $81.52   4.516%   $85.2014   $85.20   $85.20   $85.20  
  Purchase #3 $207.36   13.623%   $235.6087   $235.61   $235.60   $235.60  
  Purchase #4 $169.55   9.851%   $186.2524   $186.25   $186.25   $186.30  
  Purchase #5 $246.35   11.624%   $274.9857   $274.99   $275.00   $275.00  
  Purchase #6 $153.53   4.176%   $159.9414   $159.94   $159.95   $159.90  
  Purchase #7 $198.90   5.828%   $210.4919   $210.49   $210.50   $210.50  
  7 purchase totals = $1,178.87       $1,278.4714   $1,278.47   $1,278.50   $1,278.50