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	$22.82	7.203%	$24.4637	$24.46	$24.45	$24.50
Purchase #2	$100.31	5.457%	$105.7839	$105.78	$105.80	$105.80
Purchase #3	$91.47	9.780%	$100.4158	$100.42	$100.40	$100.40
Purchase #4	$223.82	6.855%	$239.1629	$239.16	$239.15	$239.20
Purchase #5	$26.27	6.241%	$27.9095	$27.91	$27.90	$27.90
Purchase #6	$89.84	9.522%	$98.3946	$98.39	$98.40	$98.40
Purchase #7	$139.65	4.360%	$145.7387	$145.74	$145.75	$145.70
7 purchase totals =	$694.18		$741.8691	$741.86	$741.85	$741.90