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	$24.78	12.394%	$27.8512	$27.85	$27.85	$27.90
Purchase #2	$72.66	4.679%	$76.0598	$76.06	$76.05	$76.10
Purchase #3	$24.32	6.457%	$25.8903	$25.89	$25.90	$25.90
Purchase #4	$206.63	6.633%	$220.3358	$220.34	$220.35	$220.30
Purchase #5	$102.48	9.613%	$112.3314	$112.33	$112.35	$112.30
Purchase #6	$228.48	11.818%	$255.4818	$255.48	$255.50	$255.50
Purchase #7	$40.79	11.454%	$45.4621	$45.46	$45.45	$45.50
7 purchase totals =	$700.14		$763.4124	$763.41	$763.45	$763.50