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	$152.31	11.586%	$169.9566	$169.96	$169.95	$170.00
Purchase #2	$219.57	12.519%	$247.058	$247.06	$247.05	$247.10
Purchase #3	$169.52	9.223%	$185.1548	$185.15	$185.15	$185.20
Purchase #4	$104.37	11.575%	$116.4508	$116.45	$116.45	$116.50
Purchase #5	$47.55	11.730%	$53.1276	$53.13	$53.15	$53.10
Purchase #6	$154.77	12.116%	$173.5219	$173.52	$173.50	$173.50
Purchase #7	$179.69	9.139%	$196.1119	$196.11	$196.10	$196.10
7 purchase totals =	$1,027.78		$1,141.3816	$1,141.38	$1,141.35	$1,141.50