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	$223.76	11.381%	$249.2261	$249.23	$249.25	$249.20
Purchase #2	$33.38	8.405%	$36.1856	$36.19	$36.20	$36.20
Purchase #3	$224.82	13.846%	$255.9486	$255.95	$255.95	$255.90
Purchase #4	$25.45	9.533%	$27.8761	$27.88	$27.90	$27.90
Purchase #5	$11.73	9.759%	$12.8747	$12.87	$12.85	$12.90
Purchase #6	$138.37	8.846%	$150.6102	$150.61	$150.60	$150.60
Purchase #7	$33.56	6.267%	$35.6632	$35.66	$35.65	$35.70
7 purchase totals =	$691.07		$768.3845	$768.39	$768.40	$768.40