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	$39.29	12.591%	$44.237	$44.24	$44.25	$44.20
Purchase #2	$73.78	6.770%	$78.7749	$78.77	$78.75	$78.80
Purchase #3	$87.70	4.512%	$91.657	$91.66	$91.65	$91.70
Purchase #4	$35.66	5.853%	$37.7472	$37.75	$37.75	$37.70
Purchase #5	$13.39	13.364%	$15.1794	$15.18	$15.20	$15.20
Purchase #6	$175.75	5.516%	$185.4444	$185.44	$185.45	$185.40
Purchase #7	$49.91	8.699%	$54.2517	$54.25	$54.25	$54.30
7 purchase totals =	$475.48		$507.2916	$507.29	$507.30	$507.30