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	$100.28	6.608%	$106.9065	$106.91	$106.90	$106.90
Purchase #2	$121.38	11.371%	$135.1821	$135.18	$135.20	$135.20
Purchase #3	$115.55	6.528%	$123.0931	$123.09	$123.10	$123.10
Purchase #4	$95.25	13.705%	$108.304	$108.30	$108.30	$108.30
Purchase #5	$160.85	7.655%	$173.1631	$173.16	$173.15	$173.20
Purchase #6	$70.31	11.285%	$78.2445	$78.24	$78.25	$78.20
Purchase #7	$78.99	4.805%	$82.7855	$82.79	$82.80	$82.80
7 purchase totals =	$742.61		$807.6788	$807.67	$807.70	$807.70