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	$143.80	4.675%	$150.5227	$150.52	$150.50	$150.50
Purchase #2	$115.85	10.245%	$127.7188	$127.72	$127.70	$127.70
Purchase #3	$16.37	13.710%	$18.6143	$18.61	$18.60	$18.60
Purchase #4	$29.36	7.502%	$31.5626	$31.56	$31.55	$31.60
Purchase #5	$135.37	12.611%	$152.4415	$152.44	$152.45	$152.40
Purchase #6	$170.99	6.255%	$181.6854	$181.69	$181.70	$181.70
Purchase #7	$131.95	12.828%	$148.8765	$148.88	$148.90	$148.90
7 purchase totals =	$743.69		$811.4218	$811.42	$811.40	$811.40