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	$126.99	12.419%	$142.7609	$142.76	$142.75	$142.80
Purchase #2	$56.81	4.657%	$59.4556	$59.46	$59.45	$59.50
Purchase #3	$56.40	11.108%	$62.6649	$62.66	$62.65	$62.70
Purchase #4	$83.66	10.288%	$92.2669	$92.27	$92.25	$92.30
Purchase #5	$190.40	9.562%	$208.606	$208.61	$208.60	$208.60
Purchase #6	$22.44	12.197%	$25.177	$25.18	$25.20	$25.20
Purchase #7	$228.94	8.615%	$248.6632	$248.66	$248.65	$248.70
7 purchase totals =	$765.64		$839.5945	$839.60	$839.55	$839.80