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	$29.97	12.590%	$33.7432	$33.74	$33.75	$33.70
Purchase #2	$141.68	12.519%	$159.4169	$159.42	$159.40	$159.40
Purchase #3	$149.43	7.245%	$160.2562	$160.26	$160.25	$160.30
Purchase #4	$70.63	10.664%	$78.162	$78.16	$78.15	$78.20
Purchase #5	$220.46	12.189%	$247.3319	$247.33	$247.35	$247.30
Purchase #6	$222.27	11.786%	$248.4667	$248.47	$248.45	$248.50
Purchase #7	$157.83	4.616%	$165.1154	$165.12	$165.10	$165.10
7 purchase totals =	$992.27		$1,092.4923	$1,092.50	$1,092.45	$1,092.50