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	$125.79	10.430%	$138.9099	$138.91	$138.90	$138.90
Purchase #2	$29.69	9.310%	$32.4541	$32.45	$32.45	$32.50
Purchase #3	$95.64	10.348%	$105.5368	$105.54	$105.55	$105.50
Purchase #4	$29.47	11.823%	$32.9542	$32.95	$32.95	$33.00
Purchase #5	$28.30	10.799%	$31.3561	$31.36	$31.35	$31.40
Purchase #6	$145.59	11.275%	$162.0053	$162.01	$162.00	$162.00
Purchase #7	$50.69	6.477%	$53.9732	$53.97	$53.95	$54.00
7 purchase totals =	$505.17		$557.1896	$557.19	$557.15	$557.30