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	$172.40	9.110%	$188.1056	$188.11	$188.10	$188.10
Purchase #2	$166.74	4.487%	$174.2216	$174.22	$174.20	$174.20
Purchase #3	$111.53	13.711%	$126.8219	$126.82	$126.80	$126.80
Purchase #4	$195.61	12.128%	$219.3336	$219.33	$219.35	$219.30
Purchase #5	$59.38	9.672%	$65.1232	$65.12	$65.10	$65.10
Purchase #6	$85.38	5.368%	$89.9632	$89.96	$89.95	$90.00
Purchase #7	$52.85	3.297%	$54.5925	$54.59	$54.60	$54.60
7 purchase totals =	$843.89		$918.1616	$918.15	$918.10	$918.10