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	$82.69	10.380%	$91.2732	$91.27	$91.25	$91.30
Purchase #2	$172.32	3.822%	$178.9061	$178.91	$178.90	$178.90
Purchase #3	$132.96	3.377%	$137.4501	$137.45	$137.45	$137.50
Purchase #4	$171.78	9.332%	$187.8105	$187.81	$187.80	$187.80
Purchase #5	$170.71	9.687%	$187.2467	$187.25	$187.25	$187.20
Purchase #6	$31.38	12.410%	$35.2743	$35.27	$35.25	$35.30
Purchase #7	$49.55	10.428%	$54.7171	$54.72	$54.70	$54.70
7 purchase totals =	$811.39		$872.6780	$872.68	$872.60	$872.70