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	$49.41	12.444%	$55.5586	$55.56	$55.55	$55.60
Purchase #2	$184.71	6.420%	$196.5684	$196.57	$196.55	$196.60
Purchase #3	$18.62	11.298%	$20.7237	$20.72	$20.70	$20.70
Purchase #4	$231.67	5.267%	$243.8721	$243.87	$243.85	$243.90
Purchase #5	$73.28	5.147%	$77.0517	$77.05	$77.05	$77.10
Purchase #6	$125.83	3.529%	$130.2705	$130.27	$130.25	$130.30
Purchase #7	$11.39	7.543%	$12.2491	$12.25	$12.25	$12.20
7 purchase totals =	$694.91		$736.2941	$736.29	$736.20	$736.40