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	$78.31	5.844%	$82.8864	$82.89	$82.90	$82.90
Purchase #2	$146.40	9.130%	$159.7663	$159.77	$159.75	$159.80
Purchase #3	$66.91	11.841%	$74.8328	$74.83	$74.85	$74.80
Purchase #4	$199.27	5.321%	$209.8732	$209.87	$209.85	$209.90
Purchase #5	$191.46	7.823%	$206.4379	$206.44	$206.45	$206.40
Purchase #6	$50.52	11.645%	$56.4031	$56.40	$56.40	$56.40
Purchase #7	$90.35	11.330%	$100.5867	$100.59	$100.60	$100.60
7 purchase totals =	$823.22		$890.7864	$890.79	$890.80	$890.80