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	$10.26	6.250%	$10.9013	$10.90	$10.90	$10.90
Purchase #2	$52.54	12.579%	$59.149	$59.15	$59.15	$59.10
Purchase #3	$130.77	6.579%	$139.3734	$139.37	$139.35	$139.40
Purchase #4	$169.47	3.504%	$175.4082	$175.41	$175.40	$175.40
Purchase #5	$83.60	3.841%	$86.8111	$86.81	$86.80	$86.80
Purchase #6	$185.43	4.121%	$193.0716	$193.07	$193.05	$193.10
Purchase #7	$104.55	10.466%	$115.4922	$115.49	$115.50	$115.50
7 purchase totals =	$736.62		$780.2068	$780.20	$780.15	$780.20