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	$97.37	5.106%	$102.3417	$102.34	$102.35	$102.30
Purchase #2	$80.29	12.488%	$90.3166	$90.32	$90.30	$90.30
Purchase #3	$37.86	12.576%	$42.6213	$42.62	$42.60	$42.60
Purchase #4	$117.45	5.504%	$123.9144	$123.91	$123.90	$123.90
Purchase #5	$141.31	7.222%	$151.5154	$151.52	$151.50	$151.50
Purchase #6	$36.62	8.247%	$39.6401	$39.64	$39.65	$39.60
Purchase #7	$65.27	12.650%	$73.5267	$73.53	$73.55	$73.50
7 purchase totals =	$576.17		$623.8762	$623.88	$623.85	$623.70