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	$61.40	4.556%	$64.1974	$64.20	$64.20	$64.20
Purchase #2	$50.54	5.539%	$53.3394	$53.34	$53.35	$53.30
Purchase #3	$25.68	10.295%	$28.3238	$28.32	$28.30	$28.30
Purchase #4	$119.35	7.197%	$127.9396	$127.94	$127.95	$127.90
Purchase #5	$105.26	4.255%	$109.7388	$109.74	$109.75	$109.70
Purchase #6	$25.89	8.838%	$28.1782	$28.18	$28.20	$28.20
Purchase #7	$103.64	11.267%	$115.3171	$115.32	$115.30	$115.30
7 purchase totals =	$491.76		$527.0343	$527.04	$527.05	$526.90