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	$105.40	6.731%	$112.4945	$112.49	$112.50	$112.50
Purchase #2	$189.88	5.602%	$200.5171	$200.52	$200.50	$200.50
Purchase #3	$142.49	4.614%	$149.0645	$149.06	$149.05	$149.10
Purchase #4	$48.26	11.604%	$53.8601	$53.86	$53.85	$53.90
Purchase #5	$90.95	5.579%	$96.0241	$96.02	$96.00	$96.00
Purchase #6	$137.92	7.546%	$148.3274	$148.33	$148.35	$148.30
Purchase #7	$64.28	3.233%	$66.3582	$66.36	$66.35	$66.40
7 purchase totals =	$779.18		$826.6459	$826.64	$826.60	$826.70