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	$130.27	7.149%	$139.583	$139.58	$139.60	$139.60
Purchase #2	$110.45	4.692%	$115.6323	$115.63	$115.65	$115.60
Purchase #3	$15.30	3.165%	$15.7842	$15.78	$15.80	$15.80
Purchase #4	$209.27	12.251%	$234.9077	$234.91	$234.90	$234.90
Purchase #5	$72.69	6.866%	$77.6809	$77.68	$77.70	$77.70
Purchase #6	$54.39	9.275%	$59.4347	$59.43	$59.45	$59.40
Purchase #7	$102.47	3.363%	$105.9161	$105.92	$105.90	$105.90
7 purchase totals =	$694.84		$748.9389	$748.93	$749.00	$748.90