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	$7.38	10.746%	$8.1731	$8.17	$8.15	$8.20
Purchase #2	$140.68	5.253%	$148.0699	$148.07	$148.05	$148.10
Purchase #3	$36.97	3.627%	$38.3109	$38.31	$38.30	$38.30
Purchase #4	$164.76	8.142%	$178.1748	$178.17	$178.15	$178.20
Purchase #5	$55.72	7.540%	$59.9213	$59.92	$59.90	$59.90
Purchase #6	$94.93	4.390%	$99.0974	$99.10	$99.10	$99.10
Purchase #7	$148.77	7.664%	$160.1717	$160.17	$160.15	$160.20
7 purchase totals =	$649.21		$691.9191	$691.91	$691.80	$692.00