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	$25.91	10.315%	$28.5826	$28.58	$28.60	$28.60
Purchase #2	$68.44	6.550%	$72.9228	$72.92	$72.90	$72.90
Purchase #3	$86.63	4.765%	$90.7579	$90.76	$90.75	$90.80
Purchase #4	$208.51	10.539%	$230.4849	$230.48	$230.50	$230.50
Purchase #5	$125.91	13.572%	$142.9985	$143.00	$143.00	$143.00
Purchase #6	$172.72	10.550%	$190.942	$190.94	$190.95	$190.90
Purchase #7	$167.69	4.841%	$175.8079	$175.81	$175.80	$175.80
7 purchase totals =	$855.81		$932.4966	$932.49	$932.50	$932.50