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	$121.32	4.712%	$127.0366	$127.04	$127.05	$127.00
Purchase #2	$55.34	4.738%	$57.962	$57.96	$57.95	$58.00
Purchase #3	$16.60	7.513%	$17.8472	$17.85	$17.85	$17.80
Purchase #4	$212.53	5.223%	$223.6304	$223.63	$223.65	$223.60
Purchase #5	$93.54	7.799%	$100.8352	$100.84	$100.85	$100.80
Purchase #6	$45.77	11.723%	$51.1356	$51.14	$51.15	$51.10
Purchase #7	$56.85	9.406%	$62.1973	$62.20	$62.20	$62.20
7 purchase totals =	$601.95		$640.6443	$640.66	$640.70	$640.50