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	$95.42	3.530%	$98.7883	$98.79	$98.80	$98.80
Purchase #2	$249.45	11.827%	$278.9525	$278.95	$278.95	$279.00
Purchase #3	$78.87	13.726%	$89.6957	$89.70	$89.70	$89.70
Purchase #4	$16.34	7.715%	$17.6006	$17.60	$17.60	$17.60
Purchase #5	$222.87	12.699%	$251.1723	$251.17	$251.15	$251.20
Purchase #6	$232.72	13.736%	$264.6864	$264.69	$264.70	$264.70
Purchase #7	$81.37	13.632%	$92.4624	$92.46	$92.45	$92.50
7 purchase totals =	$977.04		$1,093.3582	$1,093.36	$1,093.35	$1,093.50