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	$75.57	3.406%	$78.1439	$78.14	$78.15	$78.10
Purchase #2	$169.56	10.186%	$186.8314	$186.83	$186.85	$186.80
Purchase #3	$123.98	12.480%	$139.4527	$139.45	$139.45	$139.50
Purchase #4	$159.50	7.766%	$171.8868	$171.89	$171.90	$171.90
Purchase #5	$238.67	7.551%	$256.692	$256.69	$256.70	$256.70
Purchase #6	$46.47	6.234%	$49.3669	$49.37	$49.35	$49.40
Purchase #7	$202.72	8.147%	$219.2356	$219.24	$219.25	$219.20
7 purchase totals =	$1,016.47		$1,101.6093	$1,101.61	$1,101.65	$1,101.60