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	$122.48	11.642%	$136.7391	$136.74	$136.75	$136.70
Purchase #2	$218.34	9.418%	$238.9033	$238.90	$238.90	$238.90
Purchase #3	$212.53	4.705%	$222.5295	$222.53	$222.55	$222.50
Purchase #4	$247.37	11.341%	$275.4242	$275.42	$275.40	$275.40
Purchase #5	$58.70	4.709%	$61.4642	$61.46	$61.45	$61.50
Purchase #6	$134.32	11.444%	$149.6916	$149.69	$149.70	$149.70
Purchase #7	$181.59	11.540%	$202.5455	$202.55	$202.55	$202.50
7 purchase totals =	$1,175.33		$1,287.2974	$1,287.29	$1,287.30	$1,287.20