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	$133.41	9.144%	$145.609	$145.61	$145.60	$145.60
Purchase #2	$228.66	9.306%	$249.9391	$249.94	$249.95	$249.90
Purchase #3	$99.27	12.611%	$111.7889	$111.79	$111.80	$111.80
Purchase #4	$200.80	6.229%	$213.3078	$213.31	$213.30	$213.30
Purchase #5	$154.61	11.422%	$172.2696	$172.27	$172.25	$172.30
Purchase #6	$180.48	12.170%	$202.4444	$202.44	$202.45	$202.40
Purchase #7	$247.79	11.347%	$275.9067	$275.91	$275.90	$275.90
7 purchase totals =	$1,245.02		$1,371.2655	$1,371.27	$1,371.25	$1,371.20