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	$89.95	10.489%	$99.3849	$99.38	$99.40	$99.40
Purchase #2	$22.50	8.164%	$24.3369	$24.34	$24.35	$24.30
Purchase #3	$120.41	12.667%	$135.6623	$135.66	$135.65	$135.70
Purchase #4	$131.45	4.794%	$137.7517	$137.75	$137.75	$137.80
Purchase #5	$142.55	5.557%	$150.4715	$150.47	$150.45	$150.50
Purchase #6	$102.57	11.581%	$114.4486	$114.45	$114.45	$114.40
Purchase #7	$89.53	13.825%	$101.9075	$101.91	$101.90	$101.90
7 purchase totals =	$698.96		$763.9634	$763.96	$763.95	$764.00