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	$66.51	5.607%	$70.2392	$70.24	$70.25	$70.20
Purchase #2	$90.35	10.797%	$100.1051	$100.11	$100.10	$100.10
Purchase #3	$213.62	13.783%	$243.0632	$243.06	$243.05	$243.10
Purchase #4	$134.92	10.298%	$148.8141	$148.81	$148.80	$148.80
Purchase #5	$45.72	7.622%	$49.2048	$49.20	$49.20	$49.20
Purchase #6	$196.69	9.361%	$215.1022	$215.10	$215.10	$215.10
Purchase #7	$240.84	6.190%	$255.748	$255.75	$255.75	$255.70
7 purchase totals =	$988.65		$1,082.2766	$1,082.27	$1,082.25	$1,082.20