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	$151.73	8.848%	$165.1551	$165.16	$165.15	$165.20
Purchase #2	$50.31	8.449%	$54.5607	$54.56	$54.55	$54.60
Purchase #3	$53.50	3.786%	$55.5255	$55.53	$55.55	$55.50
Purchase #4	$136.77	8.616%	$148.5541	$148.55	$148.55	$148.60
Purchase #5	$118.43	12.797%	$133.5855	$133.59	$133.60	$133.60
Purchase #6	$67.81	13.642%	$77.0606	$77.06	$77.05	$77.10
Purchase #7	$32.62	3.798%	$33.8589	$33.86	$33.85	$33.90
7 purchase totals =	$611.17		$668.3004	$668.31	$668.30	$668.50