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 $214.57   11.720%   $239.7176   $239.72   $239.70   $239.70  
  Purchase #2 $204.63   9.794%   $224.6715   $224.67   $224.65   $224.70  
  Purchase #3 $162.64   13.728%   $184.9672   $184.97   $184.95   $185.00  
  Purchase #4 $233.28   12.355%   $262.1017   $262.10   $262.10   $262.10  
  Purchase #5 $128.97   3.399%   $133.3537   $133.35   $133.35   $133.40  
  Purchase #6 $224.72   4.543%   $234.929   $234.93   $234.95   $234.90  
  Purchase #7 $219.46   11.412%   $244.5048   $244.50   $244.50   $244.50  
  7 purchase totals = $1,388.27       $1,524.2455   $1,524.24   $1,524.20   $1,524.30