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	$90.99	5.828%	$96.2929	$96.29	$96.30	$96.30
Purchase #2	$53.69	10.132%	$59.1299	$59.13	$59.15	$59.10
Purchase #3	$117.53	5.357%	$123.8261	$123.83	$123.85	$123.80
Purchase #4	$49.33	6.311%	$52.4432	$52.44	$52.45	$52.40
Purchase #5	$128.61	6.221%	$136.6108	$136.61	$136.60	$136.60
Purchase #6	$56.52	5.502%	$59.6297	$59.63	$59.65	$59.60
Purchase #7	$143.25	3.110%	$147.7051	$147.71	$147.70	$147.70
7 purchase totals =	$639.92		$675.6377	$675.64	$675.70	$675.50