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	$12.25	13.474%	$13.9006	$13.90	$13.90	$13.90
Purchase #2	$212.62	4.543%	$222.2793	$222.28	$222.30	$222.30
Purchase #3	$106.67	4.481%	$111.4499	$111.45	$111.45	$111.40
Purchase #4	$171.87	4.115%	$178.9425	$178.94	$178.95	$178.90
Purchase #5	$116.36	9.306%	$127.1885	$127.19	$127.20	$127.20
Purchase #6	$32.58	3.709%	$33.7884	$33.79	$33.80	$33.80
Purchase #7	$134.28	6.675%	$143.2432	$143.24	$143.25	$143.20
7 purchase totals =	$786.63		$830.7924	$830.79	$830.85	$830.70