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	$73.71	7.341%	$79.1211	$79.12	$79.10	$79.10
Purchase #2	$89.38	6.458%	$95.1522	$95.15	$95.15	$95.20
Purchase #3	$64.39	4.652%	$67.3854	$67.39	$67.40	$67.40
Purchase #4	$84.40	6.741%	$90.0894	$90.09	$90.10	$90.10
Purchase #5	$85.72	7.102%	$91.8078	$91.81	$91.80	$91.80
Purchase #6	$201.49	3.530%	$208.6026	$208.60	$208.60	$208.60
Purchase #7	$197.52	12.773%	$222.7492	$222.75	$222.75	$222.70
7 purchase totals =	$796.61		$854.9077	$854.91	$854.90	$854.90