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	$88.73	12.123%	$99.4867	$99.49	$99.50	$99.50
Purchase #2	$56.76	8.425%	$61.542	$61.54	$61.55	$61.50
Purchase #3	$179.71	5.441%	$189.488	$189.49	$189.50	$189.50
Purchase #4	$54.69	8.763%	$59.4825	$59.48	$59.50	$59.50
Purchase #5	$235.25	6.454%	$250.433	$250.43	$250.45	$250.40
Purchase #6	$38.91	3.103%	$40.1174	$40.12	$40.10	$40.10
Purchase #7	$18.69	4.376%	$19.5079	$19.51	$19.50	$19.50
7 purchase totals =	$672.74		$720.0575	$720.06	$720.10	$720.00