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	$165.72	13.315%	$187.7856	$187.79	$187.80	$187.80
Purchase #2	$135.60	12.830%	$152.9975	$153.00	$153.00	$153.00
Purchase #3	$48.82	9.578%	$53.496	$53.50	$53.50	$53.50
Purchase #4	$189.39	12.772%	$213.5789	$213.58	$213.60	$213.60
Purchase #5	$159.77	8.159%	$172.8056	$172.81	$172.80	$172.80
Purchase #6	$71.39	13.139%	$80.7699	$80.77	$80.75	$80.80
Purchase #7	$246.38	6.863%	$263.2891	$263.29	$263.30	$263.30
7 purchase totals =	$1,017.07		$1,124.7226	$1,124.74	$1,124.75	$1,124.80