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	$111.72	10.532%	$123.4864	$123.49	$123.50	$123.50
Purchase #2	$114.39	3.539%	$118.4383	$118.44	$118.45	$118.40
Purchase #3	$37.34	12.828%	$42.13	$42.13	$42.15	$42.10
Purchase #4	$160.73	13.520%	$182.4607	$182.46	$182.45	$182.50
Purchase #5	$194.69	4.727%	$203.893	$203.89	$203.90	$203.90
Purchase #6	$109.45	13.207%	$123.9051	$123.91	$123.90	$123.90
Purchase #7	$170.80	8.129%	$184.6843	$184.68	$184.70	$184.70
7 purchase totals =	$899.12		$978.9978	$979.00	$979.05	$979.00