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	$185.72	13.687%	$211.1395	$211.14	$211.15	$211.10
Purchase #2	$128.31	12.433%	$144.2628	$144.26	$144.25	$144.30
Purchase #3	$6.71	10.819%	$7.436	$7.44	$7.45	$7.40
Purchase #4	$155.78	9.866%	$171.1493	$171.15	$171.15	$171.10
Purchase #5	$11.61	5.410%	$12.2381	$12.24	$12.25	$12.20
Purchase #6	$44.83	5.234%	$47.1764	$47.18	$47.20	$47.20
Purchase #7	$48.34	11.196%	$53.7521	$53.75	$53.75	$53.80
7 purchase totals =	$581.30		$647.1542	$647.16	$647.20	$647.10