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	$20.80	7.688%	$22.3991	$22.40	$22.40	$22.40
Purchase #2	$37.96	4.166%	$39.5414	$39.54	$39.55	$39.50
Purchase #3	$86.50	3.845%	$89.8259	$89.83	$89.85	$89.80
Purchase #4	$134.91	10.667%	$149.3008	$149.30	$149.30	$149.30
Purchase #5	$199.43	6.437%	$212.2673	$212.27	$212.25	$212.30
Purchase #6	$182.41	12.166%	$204.602	$204.60	$204.60	$204.60
Purchase #7	$101.91	9.702%	$111.7973	$111.80	$111.80	$111.80
7 purchase totals =	$763.92		$829.7338	$829.74	$829.75	$829.70