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	$19.33	5.148%	$20.3251	$20.33	$20.35	$20.30
Purchase #2	$86.50	4.632%	$90.5067	$90.51	$90.50	$90.50
Purchase #3	$79.85	11.790%	$89.2643	$89.26	$89.25	$89.30
Purchase #4	$67.29	10.198%	$74.1522	$74.15	$74.15	$74.20
Purchase #5	$235.52	4.619%	$246.3987	$246.40	$246.40	$246.40
Purchase #6	$86.65	9.167%	$94.5932	$94.59	$94.60	$94.60
Purchase #7	$38.58	11.606%	$43.0576	$43.06	$43.05	$43.10
7 purchase totals =	$613.72		$658.2978	$658.30	$658.30	$658.40