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	$18.55	9.320%	$20.2789	$20.28	$20.30	$20.30
Purchase #2	$73.60	7.703%	$79.2694	$79.27	$79.25	$79.30
Purchase #3	$150.41	10.394%	$166.0436	$166.04	$166.05	$166.00
Purchase #4	$62.59	4.539%	$65.431	$65.43	$65.45	$65.40
Purchase #5	$121.90	9.311%	$133.2501	$133.25	$133.25	$133.30
Purchase #6	$54.91	3.611%	$56.8928	$56.89	$56.90	$56.90
Purchase #7	$148.33	9.605%	$162.5771	$162.58	$162.60	$162.60
7 purchase totals =	$630.29		$683.7429	$683.74	$683.80	$683.80