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	$166.25	13.231%	$188.2465	$188.25	$188.25	$188.20
Purchase #2	$72.75	7.286%	$78.0506	$78.05	$78.05	$78.10
Purchase #3	$134.59	7.658%	$144.8969	$144.90	$144.90	$144.90
Purchase #4	$234.56	12.819%	$264.6282	$264.63	$264.65	$264.60
Purchase #5	$38.32	5.525%	$40.4372	$40.44	$40.45	$40.40
Purchase #6	$19.69	5.384%	$20.7501	$20.75	$20.75	$20.80
Purchase #7	$27.38	11.733%	$30.5925	$30.59	$30.60	$30.60
7 purchase totals =	$693.54		$767.6020	$767.61	$767.65	$767.60