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	$18.27	10.110%	$20.1171	$20.12	$20.10	$20.10
Purchase #2	$102.37	9.142%	$111.7287	$111.73	$111.75	$111.70
Purchase #3	$191.28	13.755%	$217.5906	$217.59	$217.60	$217.60
Purchase #4	$221.35	9.657%	$242.7258	$242.73	$242.75	$242.70
Purchase #5	$148.37	12.873%	$167.4697	$167.47	$167.45	$167.50
Purchase #6	$166.79	4.353%	$174.0504	$174.05	$174.05	$174.10
Purchase #7	$60.92	12.676%	$68.6422	$68.64	$68.65	$68.60
7 purchase totals =	$909.35		$1,002.3245	$1,002.33	$1,002.35	$1,002.30