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	$233.30	13.283%	$264.2892	$264.29	$264.30	$264.30
Purchase #2	$27.68	13.122%	$31.3122	$31.31	$31.30	$31.30
Purchase #3	$184.52	6.389%	$196.309	$196.31	$196.30	$196.30
Purchase #4	$10.69	12.832%	$12.0617	$12.06	$12.05	$12.10
Purchase #5	$39.30	7.400%	$42.2082	$42.21	$42.20	$42.20
Purchase #6	$25.39	9.202%	$27.7264	$27.73	$27.75	$27.70
Purchase #7	$114.79	6.787%	$122.5808	$122.58	$122.60	$122.60
7 purchase totals =	$635.67		$696.4875	$696.49	$696.50	$696.50