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	$71.67	9.834%	$78.718	$78.72	$78.70	$78.70
Purchase #2	$45.54	7.700%	$49.0466	$49.05	$49.05	$49.00
Purchase #3	$9.72	9.305%	$10.6244	$10.62	$10.60	$10.60
Purchase #4	$175.56	7.386%	$188.5269	$188.53	$188.55	$188.50
Purchase #5	$75.86	12.647%	$85.454	$85.45	$85.45	$85.50
Purchase #6	$109.33	7.160%	$117.158	$117.16	$117.15	$117.20
Purchase #7	$73.59	13.353%	$83.4165	$83.42	$83.40	$83.40
7 purchase totals =	$561.27		$612.9444	$612.95	$612.90	$612.90