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	$239.43	10.386%	$264.2972	$264.30	$264.30	$264.30
Purchase #2	$74.45	4.678%	$77.9328	$77.93	$77.95	$77.90
Purchase #3	$25.64	5.405%	$27.0258	$27.03	$27.05	$27.00
Purchase #4	$92.41	9.174%	$100.8877	$100.89	$100.90	$100.90
Purchase #5	$209.66	10.121%	$230.8797	$230.88	$230.90	$230.90
Purchase #6	$123.39	8.821%	$134.2742	$134.27	$134.25	$134.30
Purchase #7	$16.93	9.387%	$18.5192	$18.52	$18.50	$18.50
7 purchase totals =	$781.91		$853.8166	$853.82	$853.85	$853.80