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	$177.59	12.572%	$199.9166	$199.92	$199.90	$199.90
Purchase #2	$179.86	11.285%	$200.1572	$200.16	$200.15	$200.20
Purchase #3	$62.94	6.623%	$67.1085	$67.11	$67.10	$67.10
Purchase #4	$43.67	5.712%	$46.1644	$46.16	$46.15	$46.20
Purchase #5	$165.88	13.783%	$188.7432	$188.74	$188.75	$188.70
Purchase #6	$30.68	12.121%	$34.3987	$34.40	$34.40	$34.40
Purchase #7	$223.77	8.378%	$242.5175	$242.52	$242.50	$242.50
7 purchase totals =	$884.39		$979.0061	$979.01	$978.95	$979.00