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	$89.75	12.788%	$101.2272	$101.23	$101.25	$101.20
Purchase #2	$176.85	9.794%	$194.1707	$194.17	$194.15	$194.20
Purchase #3	$241.90	11.830%	$270.5168	$270.52	$270.50	$270.50
Purchase #4	$104.43	6.447%	$111.1626	$111.16	$111.15	$111.20
Purchase #5	$41.63	8.830%	$45.3059	$45.31	$45.30	$45.30
Purchase #6	$238.98	4.164%	$248.9311	$248.93	$248.95	$248.90
Purchase #7	$23.32	8.299%	$25.2553	$25.26	$25.25	$25.30
7 purchase totals =	$916.86		$996.5696	$996.58	$996.55	$996.60