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	$42.32	6.288%	$44.9811	$44.98	$45.00	$45.00
Purchase #2	$47.96	9.150%	$52.3483	$52.35	$52.35	$52.30
Purchase #3	$126.69	11.411%	$141.1466	$141.15	$141.15	$141.10
Purchase #4	$30.47	5.178%	$32.0477	$32.05	$32.05	$32.00
Purchase #5	$168.57	13.354%	$191.0808	$191.08	$191.10	$191.10
Purchase #6	$247.81	12.784%	$279.49	$279.49	$279.50	$279.50
Purchase #7	$67.49	10.392%	$74.5036	$74.50	$74.50	$74.50
7 purchase totals =	$731.31		$815.5981	$815.60	$815.65	$815.50