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	$127.73	11.369%	$142.2516	$142.25	$142.25	$142.30
Purchase #2	$68.80	4.185%	$71.6793	$71.68	$71.70	$71.70
Purchase #3	$58.42	5.502%	$61.6343	$61.63	$61.65	$61.60
Purchase #4	$86.52	5.801%	$91.539	$91.54	$91.55	$91.50
Purchase #5	$236.82	6.514%	$252.2465	$252.25	$252.25	$252.20
Purchase #6	$211.55	10.355%	$233.456	$233.46	$233.45	$233.50
Purchase #7	$117.73	8.268%	$127.4639	$127.46	$127.45	$127.50
7 purchase totals =	$907.57		$980.2706	$980.27	$980.30	$980.30