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	$155.71	6.597%	$165.9822	$165.98	$166.00	$166.00
Purchase #2	$184.35	6.603%	$196.5226	$196.52	$196.50	$196.50
Purchase #3	$231.44	6.232%	$245.8633	$245.86	$245.85	$245.90
Purchase #4	$148.56	3.603%	$153.9126	$153.91	$153.90	$153.90
Purchase #5	$103.80	5.387%	$109.3917	$109.39	$109.40	$109.40
Purchase #6	$58.92	13.529%	$66.8913	$66.89	$66.90	$66.90
Purchase #7	$48.91	11.218%	$54.3967	$54.40	$54.40	$54.40
7 purchase totals =	$931.69		$992.9604	$992.95	$992.95	$993.00