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	$165.82	7.666%	$178.5318	$178.53	$178.55	$178.50
Purchase #2	$38.90	8.383%	$42.161	$42.16	$42.15	$42.20
Purchase #3	$182.27	4.813%	$191.0427	$191.04	$191.05	$191.00
Purchase #4	$100.93	10.762%	$111.7921	$111.79	$111.80	$111.80
Purchase #5	$118.36	13.663%	$134.5315	$134.53	$134.55	$134.50
Purchase #6	$233.39	7.174%	$250.1334	$250.13	$250.15	$250.10
Purchase #7	$67.95	8.353%	$73.6259	$73.63	$73.65	$73.60
7 purchase totals =	$907.62		$981.8184	$981.81	$981.90	$981.70