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	$75.84	3.614%	$78.5809	$78.58	$78.60	$78.60
Purchase #2	$152.49	6.430%	$162.2951	$162.30	$162.30	$162.30
Purchase #3	$11.99	6.333%	$12.7493	$12.75	$12.75	$12.70
Purchase #4	$70.52	12.235%	$79.1481	$79.15	$79.15	$79.10
Purchase #5	$34.35	8.202%	$37.1674	$37.17	$37.15	$37.20
Purchase #6	$99.54	7.381%	$106.887	$106.89	$106.90	$106.90
Purchase #7	$156.82	6.231%	$166.5915	$166.59	$166.60	$166.60
7 purchase totals =	$601.55		$643.4193	$643.43	$643.45	$643.40