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	$81.31	10.583%	$89.915	$89.92	$89.90	$89.90
Purchase #2	$145.59	5.421%	$153.4824	$153.48	$153.50	$153.50
Purchase #3	$145.60	5.467%	$153.56	$153.56	$153.55	$153.60
Purchase #4	$133.26	12.494%	$149.9095	$149.91	$149.90	$149.90
Purchase #5	$22.59	10.418%	$24.9434	$24.94	$24.95	$24.90
Purchase #6	$72.88	12.438%	$81.9448	$81.94	$81.95	$81.90
Purchase #7	$215.72	12.680%	$243.0733	$243.07	$243.05	$243.10
7 purchase totals =	$816.95		$896.8284	$896.82	$896.80	$896.80