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	$112.62	9.344%	$123.1432	$123.14	$123.15	$123.10
Purchase #2	$143.90	11.405%	$160.3118	$160.31	$160.30	$160.30
Purchase #3	$83.72	5.206%	$88.0785	$88.08	$88.10	$88.10
Purchase #4	$53.67	4.848%	$56.2719	$56.27	$56.25	$56.30
Purchase #5	$71.70	7.685%	$77.2101	$77.21	$77.20	$77.20
Purchase #6	$145.32	10.737%	$160.923	$160.92	$160.90	$160.90
Purchase #7	$153.40	9.683%	$168.2537	$168.25	$168.25	$168.30
7 purchase totals =	$764.33		$834.1922	$834.18	$834.15	$834.20