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	$120.42	5.554%	$127.1081	$127.11	$127.10	$127.10
Purchase #2	$128.30	10.627%	$141.9344	$141.93	$141.95	$141.90
Purchase #3	$90.29	3.582%	$93.5242	$93.52	$93.50	$93.50
Purchase #4	$216.65	12.268%	$243.2286	$243.23	$243.25	$243.20
Purchase #5	$28.35	4.365%	$29.5875	$29.59	$29.60	$29.60
Purchase #6	$51.68	6.695%	$55.14	$55.14	$55.15	$55.10
Purchase #7	$156.63	3.256%	$161.7299	$161.73	$161.75	$161.70
7 purchase totals =	$792.32		$852.2527	$852.25	$852.30	$852.10