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	$117.56	8.644%	$127.7219	$127.72	$127.70	$127.70
Purchase #2	$71.25	3.504%	$73.7466	$73.75	$73.75	$73.70
Purchase #3	$217.79	12.870%	$245.8196	$245.82	$245.80	$245.80
Purchase #4	$141.56	6.763%	$151.1337	$151.13	$151.15	$151.10
Purchase #5	$241.29	3.686%	$250.1839	$250.18	$250.20	$250.20
Purchase #6	$56.64	6.515%	$60.3301	$60.33	$60.35	$60.30
Purchase #7	$81.61	10.515%	$90.1913	$90.19	$90.20	$90.20
7 purchase totals =	$927.70		$999.1271	$999.12	$999.15	$999.00