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	$63.61	11.327%	$70.8151	$70.82	$70.80	$70.80
Purchase #2	$118.31	8.181%	$127.9889	$127.99	$128.00	$128.00
Purchase #3	$240.61	8.710%	$261.5671	$261.57	$261.55	$261.60
Purchase #4	$78.62	13.811%	$89.4782	$89.48	$89.50	$89.50
Purchase #5	$104.31	8.823%	$113.5133	$113.51	$113.50	$113.50
Purchase #6	$238.95	6.521%	$254.5319	$254.53	$254.55	$254.50
Purchase #7	$60.77	7.502%	$65.329	$65.33	$65.35	$65.30
7 purchase totals =	$905.18		$983.2235	$983.23	$983.25	$983.20