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	$25.80	7.575%	$27.7544	$27.75	$27.75	$27.80
Purchase #2	$130.62	9.654%	$143.2301	$143.23	$143.25	$143.20
Purchase #3	$52.54	10.817%	$58.2233	$58.22	$58.20	$58.20
Purchase #4	$71.91	13.794%	$81.8293	$81.83	$81.85	$81.80
Purchase #5	$146.32	13.150%	$165.5611	$165.56	$165.55	$165.60
Purchase #6	$53.93	12.131%	$60.4722	$60.47	$60.45	$60.50
Purchase #7	$125.89	3.874%	$130.767	$130.77	$130.75	$130.80
7 purchase totals =	$607.01		$667.8374	$667.83	$667.80	$667.90