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	$53.81	3.345%	$55.6099	$55.61	$55.60	$55.60
Purchase #2	$220.43	3.277%	$227.6535	$227.65	$227.65	$227.70
Purchase #3	$199.95	10.728%	$221.4006	$221.40	$221.40	$221.40
Purchase #4	$210.43	5.842%	$222.7233	$222.72	$222.70	$222.70
Purchase #5	$162.86	6.484%	$173.4198	$173.42	$173.40	$173.40
Purchase #6	$31.52	6.627%	$33.6088	$33.61	$33.60	$33.60
Purchase #7	$76.33	3.487%	$78.9916	$78.99	$79.00	$79.00
7 purchase totals =	$955.33		$1,013.4075	$1,013.40	$1,013.35	$1,013.40