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	$99.33	6.596%	$105.8818	$105.88	$105.90	$105.90
Purchase #2	$74.56	3.439%	$77.1241	$77.12	$77.10	$77.10
Purchase #3	$116.92	6.849%	$124.9279	$124.93	$124.95	$124.90
Purchase #4	$190.99	4.555%	$199.6896	$199.69	$199.70	$199.70
Purchase #5	$249.93	10.235%	$275.5103	$275.51	$275.50	$275.50
Purchase #6	$116.31	5.689%	$122.9269	$122.93	$122.95	$122.90
Purchase #7	$101.65	11.556%	$113.3967	$113.40	$113.40	$113.40
7 purchase totals =	$949.69		$1,019.4573	$1,019.46	$1,019.50	$1,019.40