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	$92.39	8.390%	$100.1415	$100.14	$100.15	$100.10
Purchase #2	$54.31	9.226%	$59.3206	$59.32	$59.30	$59.30
Purchase #3	$53.83	9.315%	$58.8443	$58.84	$58.85	$58.80
Purchase #4	$53.85	11.744%	$60.1741	$60.17	$60.15	$60.20
Purchase #5	$142.69	3.512%	$147.7013	$147.70	$147.70	$147.70
Purchase #6	$53.88	8.246%	$58.3229	$58.32	$58.30	$58.30
Purchase #7	$52.83	13.102%	$59.7518	$59.75	$59.75	$59.80
7 purchase totals =	$503.78		$544.2565	$544.24	$544.20	$544.20