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	$84.78	7.429%	$91.0783	$91.08	$91.10	$91.10
Purchase #2	$176.34	9.674%	$193.3991	$193.40	$193.40	$193.40
Purchase #3	$40.55	4.643%	$42.4327	$42.43	$42.45	$42.40
Purchase #4	$211.28	8.479%	$229.1944	$229.19	$229.20	$229.20
Purchase #5	$165.45	3.803%	$171.7421	$171.74	$171.75	$171.70
Purchase #6	$133.46	13.618%	$151.6346	$151.63	$151.65	$151.60
Purchase #7	$89.89	10.123%	$98.9896	$98.99	$99.00	$99.00
7 purchase totals =	$901.75		$978.4708	$978.46	$978.55	$978.40