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	$95.90	12.784%	$108.1599	$108.16	$108.15	$108.20
Purchase #2	$212.89	4.726%	$222.9512	$222.95	$222.95	$223.00
Purchase #3	$40.51	6.739%	$43.24	$43.24	$43.25	$43.20
Purchase #4	$227.74	5.447%	$240.145	$240.15	$240.15	$240.10
Purchase #5	$113.53	3.304%	$117.281	$117.28	$117.30	$117.30
Purchase #6	$217.33	13.463%	$246.5891	$246.59	$246.60	$246.60
Purchase #7	$57.46	7.367%	$61.6931	$61.69	$61.70	$61.70
7 purchase totals =	$965.36		$1,040.0593	$1,040.06	$1,040.10	$1,040.10