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	$232.47	7.707%	$250.3865	$250.39	$250.40	$250.40
Purchase #2	$93.66	5.860%	$99.1485	$99.15	$99.15	$99.10
Purchase #3	$190.61	10.861%	$211.3122	$211.31	$211.30	$211.30
Purchase #4	$106.73	11.278%	$118.767	$118.77	$118.75	$118.80
Purchase #5	$123.41	12.676%	$139.0535	$139.05	$139.05	$139.10
Purchase #6	$62.43	13.528%	$70.8755	$70.88	$70.90	$70.90
Purchase #7	$120.42	11.406%	$134.1551	$134.16	$134.15	$134.20
7 purchase totals =	$929.73		$1,023.6983	$1,023.71	$1,023.70	$1,023.80