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	$165.78	8.526%	$179.9144	$179.91	$179.90	$179.90
Purchase #2	$104.99	7.322%	$112.6774	$112.68	$112.70	$112.70
Purchase #3	$152.68	10.239%	$168.3129	$168.31	$168.30	$168.30
Purchase #4	$161.83	10.767%	$179.2542	$179.25	$179.25	$179.30
Purchase #5	$78.44	13.436%	$88.9792	$88.98	$89.00	$89.00
Purchase #6	$162.85	6.439%	$173.3359	$173.34	$173.35	$173.30
Purchase #7	$221.99	7.388%	$238.3906	$238.39	$238.40	$238.40
7 purchase totals =	$1,048.56		$1,140.8646	$1,140.86	$1,140.90	$1,140.90