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	$84.51	4.300%	$88.1439	$88.14	$88.15	$88.10
Purchase #2	$110.46	7.217%	$118.4319	$118.43	$118.45	$118.40
Purchase #3	$90.64	8.561%	$98.3997	$98.40	$98.40	$98.40
Purchase #4	$105.66	5.830%	$111.82	$111.82	$111.80	$111.80
Purchase #5	$191.38	6.281%	$203.4006	$203.40	$203.40	$203.40
Purchase #6	$100.39	4.772%	$105.1806	$105.18	$105.20	$105.20
Purchase #7	$87.47	11.650%	$97.6603	$97.66	$97.65	$97.70
7 purchase totals =	$770.51		$823.0370	$823.03	$823.05	$823.00