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	$28.78	12.524%	$32.3844	$32.38	$32.40	$32.40
Purchase #2	$19.33	3.295%	$19.9669	$19.97	$19.95	$20.00
Purchase #3	$74.49	13.202%	$84.3242	$84.32	$84.30	$84.30
Purchase #4	$31.25	4.473%	$32.6478	$32.65	$32.65	$32.60
Purchase #5	$18.89	6.437%	$20.1059	$20.11	$20.10	$20.10
Purchase #6	$24.56	4.112%	$25.5699	$25.57	$25.55	$25.60
Purchase #7	$99.91	5.614%	$105.5189	$105.52	$105.50	$105.50
7 purchase totals =	$297.21		$320.5180	$320.52	$320.45	$320.50