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	$64.74	8.739%	$70.3976	$70.40	$70.40	$70.40
Purchase #2	$70.64	3.682%	$73.241	$73.24	$73.25	$73.20
Purchase #3	$67.98	5.154%	$71.4837	$71.48	$71.50	$71.50
Purchase #4	$197.73	8.581%	$214.6972	$214.70	$214.70	$214.70
Purchase #5	$177.57	9.752%	$194.8866	$194.89	$194.90	$194.90
Purchase #6	$40.89	4.291%	$42.6446	$42.64	$42.65	$42.60
Purchase #7	$102.31	9.192%	$111.7143	$111.71	$111.70	$111.70
7 purchase totals =	$721.86		$779.0650	$779.06	$779.10	$779.00