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	$56.52	5.621%	$59.697	$59.70	$59.70	$59.70
Purchase #2	$189.84	4.242%	$197.893	$197.89	$197.90	$197.90
Purchase #3	$49.95	6.158%	$53.0259	$53.03	$53.05	$53.00
Purchase #4	$88.41	12.839%	$99.761	$99.76	$99.75	$99.80
Purchase #5	$191.97	7.192%	$205.7765	$205.78	$205.80	$205.80
Purchase #6	$20.67	7.144%	$22.1467	$22.15	$22.15	$22.10
Purchase #7	$27.92	12.177%	$31.3198	$31.32	$31.30	$31.30
7 purchase totals =	$625.28		$669.6199	$669.63	$669.65	$669.60