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	$108.86	10.459%	$120.2457	$120.25	$120.25	$120.20
Purchase #2	$124.90	13.354%	$141.5791	$141.58	$141.60	$141.60
Purchase #3	$240.72	6.202%	$255.6495	$255.65	$255.65	$255.60
Purchase #4	$249.36	6.367%	$265.2368	$265.24	$265.25	$265.20
Purchase #5	$126.29	10.249%	$139.2335	$139.23	$139.25	$139.20
Purchase #6	$93.72	5.801%	$99.1567	$99.16	$99.15	$99.20
Purchase #7	$40.55	11.200%	$45.0916	$45.09	$45.10	$45.10
7 purchase totals =	$984.40		$1,066.1929	$1,066.20	$1,066.25	$1,066.10