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 $239.80   11.115%   $266.4538   $266.45   $266.45   $266.50  
  Purchase #2 $126.67   10.268%   $139.6765   $139.68   $139.70   $139.70  
  Purchase #3 $231.42   10.593%   $255.9343   $255.93   $255.95   $255.90  
  Purchase #4 $246.41   13.526%   $279.7394   $279.74   $279.75   $279.70  
  Purchase #5 $26.61   4.185%   $27.7236   $27.72   $27.70   $27.70  
  Purchase #6 $177.76   6.240%   $188.8522   $188.85   $188.85   $188.90  
  Purchase #7 $222.90   10.417%   $246.1195   $246.12   $246.10   $246.10  
  7 purchase totals = $1,271.57       $1,404.4993   $1,404.49   $1,404.50   $1,404.50