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	$92.90	7.819%	$100.1639	$100.16	$100.15	$100.20
Purchase #2	$81.30	8.453%	$88.1723	$88.17	$88.15	$88.20
Purchase #3	$128.86	12.178%	$144.5526	$144.55	$144.55	$144.60
Purchase #4	$139.30	4.764%	$145.9363	$145.94	$145.95	$145.90
Purchase #5	$28.42	13.263%	$32.1893	$32.19	$32.20	$32.20
Purchase #6	$70.99	9.732%	$77.8987	$77.90	$77.90	$77.90
Purchase #7	$147.60	8.792%	$160.577	$160.58	$160.60	$160.60
7 purchase totals =	$689.37		$749.4901	$749.49	$749.50	$749.60