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	$183.64	7.105%	$196.6876	$196.69	$196.70	$196.70
Purchase #2	$105.71	12.448%	$118.8688	$118.87	$118.85	$118.90
Purchase #3	$175.98	10.741%	$194.882	$194.88	$194.90	$194.90
Purchase #4	$205.44	10.739%	$227.5022	$227.50	$227.50	$227.50
Purchase #5	$178.88	3.363%	$184.8957	$184.90	$184.90	$184.90
Purchase #6	$7.39	9.621%	$8.101	$8.10	$8.10	$8.10
Purchase #7	$7.62	4.437%	$7.9581	$7.96	$7.95	$8.00
7 purchase totals =	$864.66		$938.8954	$938.90	$938.90	$939.00