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	$136.43	13.255%	$154.5138	$154.51	$154.50	$154.50
Purchase #2	$41.62	6.571%	$44.3549	$44.35	$44.35	$44.40
Purchase #3	$214.96	13.846%	$244.7234	$244.72	$244.70	$244.70
Purchase #4	$71.51	13.172%	$80.9293	$80.93	$80.95	$80.90
Purchase #5	$199.89	7.819%	$215.5194	$215.52	$215.50	$215.50
Purchase #6	$73.77	11.210%	$82.0396	$82.04	$82.05	$82.00
Purchase #7	$195.68	11.248%	$217.6901	$217.69	$217.70	$217.70
7 purchase totals =	$933.86		$1,039.7705	$1,039.76	$1,039.75	$1,039.70