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	$99.43	4.793%	$104.1957	$104.20	$104.20	$104.20
Purchase #2	$19.98	10.321%	$22.0421	$22.04	$22.05	$22.00
Purchase #3	$48.28	10.283%	$53.2446	$53.24	$53.25	$53.20
Purchase #4	$39.66	10.686%	$43.8981	$43.90	$43.90	$43.90
Purchase #5	$87.45	12.433%	$98.3227	$98.32	$98.30	$98.30
Purchase #6	$36.89	9.654%	$40.4514	$40.45	$40.45	$40.50
Purchase #7	$7.91	6.544%	$8.4276	$8.43	$8.45	$8.40
7 purchase totals =	$339.60		$370.5822	$370.58	$370.60	$370.50