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	$250.53	5.547%	$264.4269	$264.43	$264.45	$264.40
Purchase #2	$35.66	10.695%	$39.4738	$39.47	$39.45	$39.50
Purchase #3	$85.75	7.104%	$91.8417	$91.84	$91.85	$91.80
Purchase #4	$18.54	10.858%	$20.5531	$20.55	$20.55	$20.60
Purchase #5	$148.55	5.209%	$156.288	$156.29	$156.30	$156.30
Purchase #6	$105.52	8.812%	$114.8184	$114.82	$114.80	$114.80
Purchase #7	$127.40	13.640%	$144.7774	$144.78	$144.80	$144.80
7 purchase totals =	$771.95		$832.1793	$832.18	$832.20	$832.20