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	$17.92	11.838%	$20.0414	$20.04	$20.05	$20.00
Purchase #2	$45.67	10.486%	$50.459	$50.46	$50.45	$50.50
Purchase #3	$10.67	5.766%	$11.2852	$11.29	$11.30	$11.30
Purchase #4	$146.37	6.588%	$156.0129	$156.01	$156.00	$156.00
Purchase #5	$6.57	12.347%	$7.3812	$7.38	$7.40	$7.40
Purchase #6	$73.32	4.591%	$76.6861	$76.69	$76.70	$76.70
Purchase #7	$39.87	5.602%	$42.1035	$42.10	$42.10	$42.10
7 purchase totals =	$340.39		$363.9693	$363.97	$364.00	$364.00