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	$93.78	6.678%	$100.0426	$100.04	$100.05	$100.00
Purchase #2	$230.25	3.134%	$237.466	$237.47	$237.45	$237.50
Purchase #3	$81.69	5.109%	$85.8635	$85.86	$85.85	$85.90
Purchase #4	$162.48	8.152%	$175.7254	$175.73	$175.75	$175.70
Purchase #5	$14.31	6.831%	$15.2875	$15.29	$15.30	$15.30
Purchase #6	$137.61	5.651%	$145.3863	$145.39	$145.40	$145.40
Purchase #7	$249.55	12.653%	$281.1256	$281.13	$281.15	$281.10
7 purchase totals =	$969.67		$1,040.8969	$1,040.91	$1,040.95	$1,040.90