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	$38.74	3.642%	$40.1509	$40.15	$40.15	$40.20
Purchase #2	$73.37	9.237%	$80.1472	$80.15	$80.15	$80.10
Purchase #3	$105.80	4.558%	$110.6224	$110.62	$110.60	$110.60
Purchase #4	$87.65	8.470%	$95.074	$95.07	$95.05	$95.10
Purchase #5	$35.35	5.606%	$37.3317	$37.33	$37.35	$37.30
Purchase #6	$200.95	8.132%	$217.2913	$217.29	$217.30	$217.30
Purchase #7	$137.61	3.421%	$142.3176	$142.32	$142.30	$142.30
7 purchase totals =	$679.47		$722.9351	$722.93	$722.90	$722.90