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	$41.36	3.701%	$42.8907	$42.89	$42.90	$42.90
Purchase #2	$105.45	7.396%	$113.2491	$113.25	$113.25	$113.20
Purchase #3	$88.72	3.860%	$92.1446	$92.14	$92.15	$92.10
Purchase #4	$150.86	5.311%	$158.8722	$158.87	$158.85	$158.90
Purchase #5	$34.25	11.387%	$38.15	$38.15	$38.15	$38.20
Purchase #6	$147.95	10.110%	$162.9077	$162.91	$162.90	$162.90
Purchase #7	$112.28	4.293%	$117.1002	$117.10	$117.10	$117.10
7 purchase totals =	$680.87		$725.3145	$725.31	$725.30	$725.30