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	$78.69	12.228%	$88.3122	$88.31	$88.30	$88.30
Purchase #2	$105.63	11.279%	$117.544	$117.54	$117.55	$117.50
Purchase #3	$78.45	7.133%	$84.0458	$84.05	$84.05	$84.00
Purchase #4	$71.52	9.434%	$78.2672	$78.27	$78.25	$78.30
Purchase #5	$172.34	6.863%	$184.1677	$184.17	$184.15	$184.20
Purchase #6	$112.26	5.582%	$118.5264	$118.53	$118.55	$118.50
Purchase #7	$179.91	11.491%	$200.5835	$200.58	$200.60	$200.60
7 purchase totals =	$798.80		$871.4468	$871.45	$871.45	$871.40