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	$196.53	13.556%	$223.1716	$223.17	$223.15	$223.20
Purchase #2	$60.61	8.736%	$65.9049	$65.90	$65.90	$65.90
Purchase #3	$208.85	10.854%	$231.5186	$231.52	$231.50	$231.50
Purchase #4	$159.51	6.872%	$170.4715	$170.47	$170.45	$170.50
Purchase #5	$231.60	8.487%	$251.2559	$251.26	$251.25	$251.30
Purchase #6	$62.62	3.668%	$64.9169	$64.92	$64.90	$64.90
Purchase #7	$113.40	9.554%	$124.2342	$124.23	$124.25	$124.20
7 purchase totals =	$1,033.12		$1,131.4736	$1,131.47	$1,131.40	$1,131.50