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	$29.44	3.816%	$30.5634	$30.56	$30.55	$30.60
Purchase #2	$50.66	9.324%	$55.3835	$55.38	$55.40	$55.40
Purchase #3	$33.61	10.333%	$37.0829	$37.08	$37.10	$37.10
Purchase #4	$54.72	13.558%	$62.1389	$62.14	$62.15	$62.10
Purchase #5	$21.83	13.309%	$24.7354	$24.74	$24.75	$24.70
Purchase #6	$140.94	6.552%	$150.1744	$150.17	$150.15	$150.20
Purchase #7	$48.42	11.240%	$53.8624	$53.86	$53.85	$53.90
7 purchase totals =	$379.62		$413.9409	$413.93	$413.95	$414.00