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	$81.92	10.140%	$90.2267	$90.23	$90.25	$90.20
Purchase #2	$158.92	4.715%	$166.4131	$166.41	$166.40	$166.40
Purchase #3	$52.99	4.760%	$55.5123	$55.51	$55.50	$55.50
Purchase #4	$148.50	7.109%	$159.0569	$159.06	$159.05	$159.10
Purchase #5	$125.29	5.512%	$132.196	$132.20	$132.20	$132.20
Purchase #6	$24.92	8.476%	$27.0322	$27.03	$27.05	$27.00
Purchase #7	$53.95	4.407%	$56.3276	$56.33	$56.35	$56.30
7 purchase totals =	$646.49		$686.7648	$686.77	$686.80	$686.70