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	$130.70	6.634%	$139.3706	$139.37	$139.35	$139.40
Purchase #2	$50.36	3.219%	$51.9811	$51.98	$52.00	$52.00
Purchase #3	$223.80	4.773%	$234.482	$234.48	$234.50	$234.50
Purchase #4	$99.40	3.718%	$103.0957	$103.10	$103.10	$103.10
Purchase #5	$135.28	6.667%	$144.2991	$144.30	$144.30	$144.30
Purchase #6	$244.72	13.226%	$277.0867	$277.09	$277.10	$277.10
Purchase #7	$185.98	7.554%	$200.0289	$200.03	$200.05	$200.00
7 purchase totals =	$1,070.24		$1,150.3441	$1,150.35	$1,150.40	$1,150.40