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	$167.45	7.318%	$179.704	$179.70	$179.70	$179.70
Purchase #2	$30.94	10.607%	$34.2218	$34.22	$34.20	$34.20
Purchase #3	$66.51	7.549%	$71.5308	$71.53	$71.55	$71.50
Purchase #4	$102.57	11.691%	$114.5615	$114.56	$114.55	$114.60
Purchase #5	$77.28	5.111%	$81.2298	$81.23	$81.25	$81.20
Purchase #6	$74.57	10.170%	$82.1538	$82.15	$82.15	$82.20
Purchase #7	$147.53	13.760%	$167.8301	$167.83	$167.85	$167.80
7 purchase totals =	$666.85		$731.2318	$731.22	$731.25	$731.20