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	$235.42	12.400%	$264.6121	$264.61	$264.60	$264.60
Purchase #2	$9.73	6.710%	$10.3829	$10.38	$10.40	$10.40
Purchase #3	$29.96	11.753%	$33.4812	$33.48	$33.50	$33.50
Purchase #4	$86.99	5.353%	$91.6466	$91.65	$91.65	$91.60
Purchase #5	$20.40	8.339%	$22.1012	$22.10	$22.10	$22.10
Purchase #6	$231.98	7.138%	$248.5387	$248.54	$248.55	$248.50
Purchase #7	$118.29	7.811%	$127.5296	$127.53	$127.55	$127.50
7 purchase totals =	$732.77		$798.2923	$798.29	$798.35	$798.20