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	$170.55	7.446%	$183.2492	$183.25	$183.25	$183.20
Purchase #2	$42.31	7.277%	$45.3889	$45.39	$45.40	$45.40
Purchase #3	$220.87	13.613%	$250.937	$250.94	$250.95	$250.90
Purchase #4	$243.79	6.389%	$259.3657	$259.37	$259.35	$259.40
Purchase #5	$17.31	5.849%	$18.3225	$18.32	$18.30	$18.30
Purchase #6	$178.80	6.133%	$189.7658	$189.77	$189.75	$189.80
Purchase #7	$46.73	11.776%	$52.2329	$52.23	$52.25	$52.20
7 purchase totals =	$920.36		$999.2620	$999.27	$999.25	$999.20