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	$26.85	4.290%	$28.0019	$28.00	$28.00	$28.00
Purchase #2	$54.82	7.742%	$59.0642	$59.06	$59.05	$59.10
Purchase #3	$155.60	11.689%	$173.7881	$173.79	$173.80	$173.80
Purchase #4	$38.50	10.440%	$42.5194	$42.52	$42.50	$42.50
Purchase #5	$155.75	4.435%	$162.6575	$162.66	$162.65	$162.70
Purchase #6	$155.64	4.475%	$162.6049	$162.60	$162.60	$162.60
Purchase #7	$229.82	8.498%	$249.3501	$249.35	$249.35	$249.40
7 purchase totals =	$816.98		$877.9861	$877.98	$877.95	$878.10