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	$133.68	4.276%	$139.3962	$139.40	$139.40	$139.40
Purchase #2	$91.73	4.546%	$95.9	$95.90	$95.90	$95.90
Purchase #3	$78.94	11.626%	$88.1176	$88.12	$88.10	$88.10
Purchase #4	$40.40	5.862%	$42.7682	$42.77	$42.75	$42.80
Purchase #5	$13.60	9.108%	$14.8387	$14.84	$14.85	$14.80
Purchase #6	$35.58	6.615%	$37.9336	$37.93	$37.95	$37.90
Purchase #7	$34.88	5.796%	$36.9016	$36.90	$36.90	$36.90
7 purchase totals =	$428.81		$455.8559	$455.86	$455.85	$455.80