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	$227.31	8.346%	$246.2813	$246.28	$246.30	$246.30
Purchase #2	$223.75	3.633%	$231.8788	$231.88	$231.90	$231.90
Purchase #3	$246.74	7.340%	$264.8507	$264.85	$264.85	$264.90
Purchase #4	$204.57	11.841%	$228.7931	$228.79	$228.80	$228.80
Purchase #5	$12.78	6.576%	$13.6204	$13.62	$13.60	$13.60
Purchase #6	$34.33	10.853%	$38.0558	$38.06	$38.05	$38.10
Purchase #7	$55.29	13.731%	$62.8819	$62.88	$62.90	$62.90
7 purchase totals =	$1,004.77		$1,086.3620	$1,086.36	$1,086.40	$1,086.50