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	$139.44	5.345%	$146.8931	$146.89	$146.90	$146.90
Purchase #2	$122.30	7.209%	$131.1166	$131.12	$131.10	$131.10
Purchase #3	$234.98	10.133%	$258.7905	$258.79	$258.80	$258.80
Purchase #4	$183.49	9.518%	$200.9546	$200.95	$200.95	$201.00
Purchase #5	$137.72	12.164%	$154.4723	$154.47	$154.45	$154.50
Purchase #6	$120.30	13.104%	$136.0641	$136.06	$136.05	$136.10
Purchase #7	$147.25	6.554%	$156.9008	$156.90	$156.90	$156.90
7 purchase totals =	$1,085.48		$1,185.1920	$1,185.18	$1,185.15	$1,185.30