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	$57.65	12.358%	$64.7744	$64.77	$64.75	$64.80
Purchase #2	$81.26	10.749%	$89.9946	$89.99	$90.00	$90.00
Purchase #3	$112.70	8.485%	$122.2626	$122.26	$122.25	$122.30
Purchase #4	$134.29	9.697%	$147.3121	$147.31	$147.30	$147.30
Purchase #5	$76.46	11.683%	$85.3928	$85.39	$85.40	$85.40
Purchase #6	$43.92	4.189%	$45.7598	$45.76	$45.75	$45.80
Purchase #7	$5.54	5.710%	$5.8563	$5.86	$5.85	$5.90
7 purchase totals =	$511.82		$561.3526	$561.34	$561.30	$561.50