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	$37.92	10.449%	$41.8823	$41.88	$41.90	$41.90
Purchase #2	$91.81	5.704%	$97.0468	$97.05	$97.05	$97.00
Purchase #3	$136.71	12.378%	$153.632	$153.63	$153.65	$153.60
Purchase #4	$250.99	10.578%	$277.5397	$277.54	$277.55	$277.50
Purchase #5	$94.58	4.313%	$98.6592	$98.66	$98.65	$98.70
Purchase #6	$98.75	12.872%	$111.4611	$111.46	$111.45	$111.50
Purchase #7	$123.80	12.397%	$139.1475	$139.15	$139.15	$139.10
7 purchase totals =	$834.56		$919.3686	$919.37	$919.40	$919.30