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	$171.88	11.549%	$191.7304	$191.73	$191.75	$191.70
Purchase #2	$127.56	3.842%	$132.4609	$132.46	$132.45	$132.50
Purchase #3	$84.33	9.252%	$92.1322	$92.13	$92.15	$92.10
Purchase #4	$34.40	3.291%	$35.5321	$35.53	$35.55	$35.50
Purchase #5	$34.63	7.255%	$37.1424	$37.14	$37.15	$37.10
Purchase #6	$51.98	7.846%	$56.0584	$56.06	$56.05	$56.10
Purchase #7	$10.72	3.175%	$11.0604	$11.06	$11.05	$11.10
7 purchase totals =	$515.50		$556.1168	$556.11	$556.15	$556.10