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	$170.61	10.122%	$187.8791	$187.88	$187.90	$187.90
Purchase #2	$108.57	3.646%	$112.5285	$112.53	$112.55	$112.50
Purchase #3	$239.46	13.851%	$272.6276	$272.63	$272.65	$272.60
Purchase #4	$242.79	5.302%	$255.6627	$255.66	$255.65	$255.70
Purchase #5	$150.78	9.491%	$165.0905	$165.09	$165.10	$165.10
Purchase #6	$88.62	13.270%	$100.3799	$100.38	$100.40	$100.40
Purchase #7	$98.35	10.861%	$109.0318	$109.03	$109.05	$109.00
7 purchase totals =	$1,099.18		$1,203.2001	$1,203.20	$1,203.30	$1,203.20