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	$84.39	8.563%	$91.6163	$91.62	$91.60	$91.60
Purchase #2	$159.75	13.498%	$181.3131	$181.31	$181.30	$181.30
Purchase #3	$225.29	5.445%	$237.557	$237.56	$237.55	$237.60
Purchase #4	$223.38	6.251%	$237.3435	$237.34	$237.35	$237.30
Purchase #5	$146.72	13.627%	$166.7135	$166.71	$166.70	$166.70
Purchase #6	$89.35	12.652%	$100.6546	$100.65	$100.65	$100.70
Purchase #7	$77.46	9.635%	$84.9233	$84.92	$84.90	$84.90
7 purchase totals =	$1,006.34		$1,100.1213	$1,100.11	$1,100.05	$1,100.10