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	$99.52	4.763%	$104.2601	$104.26	$104.25	$104.30
Purchase #2	$127.43	11.181%	$141.6779	$141.68	$141.70	$141.70
Purchase #3	$18.86	8.583%	$20.4788	$20.48	$20.50	$20.50
Purchase #4	$108.39	4.693%	$113.4767	$113.48	$113.50	$113.50
Purchase #5	$215.62	12.249%	$242.0313	$242.03	$242.05	$242.00
Purchase #6	$91.49	3.736%	$94.9081	$94.91	$94.90	$94.90
Purchase #7	$163.42	9.832%	$179.4875	$179.49	$179.50	$179.50
7 purchase totals =	$824.73		$896.3204	$896.33	$896.40	$896.40