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	$7.50	7.754%	$8.0816	$8.08	$8.10	$8.10
Purchase #2	$161.98	4.677%	$169.5558	$169.56	$169.55	$169.60
Purchase #3	$243.25	6.603%	$259.3118	$259.31	$259.30	$259.30
Purchase #4	$105.70	5.524%	$111.5389	$111.54	$111.55	$111.50
Purchase #5	$162.62	4.119%	$169.3183	$169.32	$169.30	$169.30
Purchase #6	$91.56	10.620%	$101.2837	$101.28	$101.30	$101.30
Purchase #7	$94.68	6.399%	$100.7386	$100.74	$100.75	$100.70
7 purchase totals =	$867.29		$919.8287	$919.83	$919.85	$919.80