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	$15.46	13.354%	$17.5245	$17.52	$17.50	$17.50
Purchase #2	$19.54	3.758%	$20.2743	$20.27	$20.25	$20.30
Purchase #3	$192.95	13.153%	$218.3287	$218.33	$218.35	$218.30
Purchase #4	$105.57	4.248%	$110.0546	$110.05	$110.05	$110.10
Purchase #5	$101.52	13.244%	$114.9653	$114.97	$114.95	$115.00
Purchase #6	$60.25	11.392%	$67.1137	$67.11	$67.10	$67.10
Purchase #7	$210.82	5.593%	$222.6112	$222.61	$222.60	$222.60
7 purchase totals =	$706.11		$770.8723	$770.86	$770.80	$770.90