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	$24.76	10.347%	$27.3219	$27.32	$27.30	$27.30
Purchase #2	$171.98	4.483%	$179.6899	$179.69	$179.70	$179.70
Purchase #3	$241.52	11.726%	$269.8406	$269.84	$269.85	$269.80
Purchase #4	$174.59	9.234%	$190.7116	$190.71	$190.70	$190.70
Purchase #5	$40.42	5.635%	$42.6977	$42.70	$42.70	$42.70
Purchase #6	$67.79	8.380%	$73.4708	$73.47	$73.45	$73.50
Purchase #7	$46.76	8.612%	$50.787	$50.79	$50.80	$50.80
7 purchase totals =	$767.82		$834.5195	$834.52	$834.50	$834.50