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	$54.73	7.428%	$58.7953	$58.80	$58.80	$58.80
Purchase #2	$102.47	5.533%	$108.1397	$108.14	$108.15	$108.10
Purchase #3	$111.68	13.792%	$127.0829	$127.08	$127.10	$127.10
Purchase #4	$166.61	10.741%	$184.5056	$184.51	$184.50	$184.50
Purchase #5	$69.89	11.272%	$77.768	$77.77	$77.75	$77.80
Purchase #6	$122.79	13.489%	$139.3531	$139.35	$139.35	$139.40
Purchase #7	$93.35	13.813%	$106.2444	$106.24	$106.25	$106.20
7 purchase totals =	$721.52		$801.8890	$801.89	$801.90	$801.90