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	$90.61	10.514%	$100.1367	$100.14	$100.15	$100.10
Purchase #2	$209.89	3.821%	$217.9099	$217.91	$217.90	$217.90
Purchase #3	$133.96	12.143%	$150.2268	$150.23	$150.25	$150.20
Purchase #4	$45.84	9.290%	$50.0985	$50.10	$50.10	$50.10
Purchase #5	$27.45	12.650%	$30.9224	$30.92	$30.90	$30.90
Purchase #6	$174.77	6.411%	$185.9745	$185.97	$185.95	$186.00
Purchase #7	$12.33	4.659%	$12.9045	$12.90	$12.90	$12.90
7 purchase totals =	$694.85		$748.1733	$748.17	$748.15	$748.10