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	$86.84	3.520%	$89.8968	$89.90	$89.90	$89.90
Purchase #2	$235.94	9.519%	$258.3991	$258.40	$258.40	$258.40
Purchase #3	$128.38	13.492%	$145.701	$145.70	$145.70	$145.70
Purchase #4	$76.38	9.853%	$83.9057	$83.91	$83.90	$83.90
Purchase #5	$88.63	3.170%	$91.4396	$91.44	$91.45	$91.40
Purchase #6	$154.67	7.209%	$165.8202	$165.82	$165.80	$165.80
Purchase #7	$248.66	3.211%	$256.6445	$256.64	$256.65	$256.60
7 purchase totals =	$1,019.50		$1,091.8069	$1,091.81	$1,091.80	$1,091.70