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	$40.93	4.487%	$42.7665	$42.77	$42.75	$42.80
Purchase #2	$219.49	4.293%	$228.9127	$228.91	$228.90	$228.90
Purchase #3	$9.93	9.678%	$10.891	$10.89	$10.90	$10.90
Purchase #4	$229.39	8.696%	$249.3378	$249.34	$249.35	$249.30
Purchase #5	$216.50	3.280%	$223.6012	$223.60	$223.60	$223.60
Purchase #6	$144.27	6.593%	$153.7817	$153.78	$153.80	$153.80
Purchase #7	$104.27	7.609%	$112.2039	$112.20	$112.20	$112.20
7 purchase totals =	$964.78		$1,021.4948	$1,021.49	$1,021.50	$1,021.50