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	$79.76	11.854%	$89.2148	$89.21	$89.20	$89.20
Purchase #2	$158.93	9.576%	$174.1491	$174.15	$174.15	$174.10
Purchase #3	$216.29	5.527%	$228.2443	$228.24	$228.25	$228.20
Purchase #4	$240.66	7.839%	$259.5253	$259.53	$259.55	$259.50
Purchase #5	$172.81	13.845%	$196.7355	$196.74	$196.75	$196.70
Purchase #6	$227.70	10.561%	$251.7474	$251.75	$251.75	$251.70
Purchase #7	$45.46	11.800%	$50.8243	$50.82	$50.80	$50.80
7 purchase totals =	$1,141.61		$1,250.4407	$1,250.44	$1,250.45	$1,250.20