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	$181.29	12.190%	$203.3893	$203.39	$203.40	$203.40
Purchase #2	$137.27	4.874%	$143.9605	$143.96	$143.95	$144.00
Purchase #3	$145.56	12.787%	$164.1728	$164.17	$164.15	$164.20
Purchase #4	$233.44	9.510%	$255.6401	$255.64	$255.65	$255.60
Purchase #5	$104.80	12.674%	$118.0824	$118.08	$118.10	$118.10
Purchase #6	$93.53	10.620%	$103.4629	$103.46	$103.45	$103.50
Purchase #7	$152.31	12.324%	$171.0807	$171.08	$171.10	$171.10
7 purchase totals =	$1,048.20		$1,159.7887	$1,159.78	$1,159.80	$1,159.90