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	$133.71	4.566%	$139.8152	$139.82	$139.80	$139.80
Purchase #2	$232.31	11.123%	$258.1498	$258.15	$258.15	$258.10
Purchase #3	$37.73	5.672%	$39.87	$39.87	$39.85	$39.90
Purchase #4	$238.48	11.381%	$265.6214	$265.62	$265.60	$265.60
Purchase #5	$9.86	7.755%	$10.6246	$10.62	$10.60	$10.60
Purchase #6	$76.83	12.797%	$86.6619	$86.66	$86.65	$86.70
Purchase #7	$72.85	13.519%	$82.6986	$82.70	$82.70	$82.70
7 purchase totals =	$801.77		$883.4415	$883.44	$883.35	$883.40