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	$38.40	11.827%	$42.9416	$42.94	$42.95	$42.90
Purchase #2	$206.27	11.233%	$229.4403	$229.44	$229.45	$229.40
Purchase #3	$94.39	11.332%	$105.0863	$105.09	$105.10	$105.10
Purchase #4	$156.28	13.568%	$177.4841	$177.48	$177.50	$177.50
Purchase #5	$19.66	11.290%	$21.8796	$21.88	$21.90	$21.90
Purchase #6	$85.81	6.836%	$91.676	$91.68	$91.70	$91.70
Purchase #7	$11.37	3.763%	$11.7979	$11.80	$11.80	$11.80
7 purchase totals =	$612.18		$680.3058	$680.31	$680.40	$680.30