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	$80.48	11.692%	$89.8897	$89.89	$89.90	$89.90
Purchase #2	$115.98	12.371%	$130.3279	$130.33	$130.35	$130.30
Purchase #3	$248.28	9.583%	$272.0727	$272.07	$272.05	$272.10
Purchase #4	$140.66	7.144%	$150.7088	$150.71	$150.70	$150.70
Purchase #5	$91.52	7.253%	$98.1579	$98.16	$98.15	$98.20
Purchase #6	$52.82	13.433%	$59.9153	$59.92	$59.90	$59.90
Purchase #7	$85.54	12.408%	$96.1538	$96.15	$96.15	$96.20
7 purchase totals =	$815.28		$897.2261	$897.23	$897.20	$897.30