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	$61.61	7.284%	$66.0977	$66.10	$66.10	$66.10
Purchase #2	$244.50	11.370%	$272.2997	$272.30	$272.30	$272.30
Purchase #3	$222.94	13.768%	$253.6344	$253.63	$253.65	$253.60
Purchase #4	$145.86	12.610%	$164.2529	$164.25	$164.25	$164.30
Purchase #5	$107.36	8.154%	$116.1141	$116.11	$116.10	$116.10
Purchase #6	$209.72	8.531%	$227.6112	$227.61	$227.60	$227.60
Purchase #7	$81.72	11.782%	$91.3483	$91.35	$91.35	$91.30
7 purchase totals =	$1,073.71		$1,191.3583	$1,191.35	$1,191.35	$1,191.30