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	$243.77	7.406%	$261.8236	$261.82	$261.80	$261.80
Purchase #2	$137.66	11.786%	$153.8846	$153.88	$153.90	$153.90
Purchase #3	$91.87	13.338%	$104.1236	$104.12	$104.10	$104.10
Purchase #4	$134.26	13.314%	$152.1354	$152.14	$152.15	$152.10
Purchase #5	$81.79	9.243%	$89.3498	$89.35	$89.35	$89.30
Purchase #6	$150.82	5.570%	$159.2207	$159.22	$159.20	$159.20
Purchase #7	$217.36	9.846%	$238.7613	$238.76	$238.75	$238.80
7 purchase totals =	$1,057.53		$1,159.2990	$1,159.29	$1,159.25	$1,159.20