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	$135.34	12.618%	$152.4172	$152.42	$152.40	$152.40
Purchase #2	$29.90	7.460%	$32.1305	$32.13	$32.15	$32.10
Purchase #3	$137.43	10.599%	$151.9962	$152.00	$152.00	$152.00
Purchase #4	$6.93	6.722%	$7.3958	$7.40	$7.40	$7.40
Purchase #5	$182.67	7.624%	$196.5968	$196.60	$196.60	$196.60
Purchase #6	$131.95	4.591%	$138.0078	$138.01	$138.00	$138.00
Purchase #7	$104.61	6.766%	$111.6879	$111.69	$111.70	$111.70
7 purchase totals =	$728.83		$790.2322	$790.25	$790.25	$790.20