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	$89.41	10.790%	$99.0573	$99.06	$99.05	$99.10
Purchase #2	$219.79	6.210%	$233.439	$233.44	$233.45	$233.40
Purchase #3	$130.47	10.568%	$144.2581	$144.26	$144.25	$144.30
Purchase #4	$21.70	5.742%	$22.946	$22.95	$22.95	$22.90
Purchase #5	$98.43	13.494%	$111.7121	$111.71	$111.70	$111.70
Purchase #6	$74.47	10.433%	$82.2395	$82.24	$82.25	$82.20
Purchase #7	$147.52	6.653%	$157.3345	$157.33	$157.35	$157.30
7 purchase totals =	$781.79		$850.9865	$850.99	$851.00	$850.90