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	$33.50	11.299%	$37.2852	$37.29	$37.30	$37.30
Purchase #2	$197.27	13.844%	$224.5801	$224.58	$224.60	$224.60
Purchase #3	$59.94	7.758%	$64.5901	$64.59	$64.60	$64.60
Purchase #4	$84.28	10.122%	$92.8108	$92.81	$92.80	$92.80
Purchase #5	$36.98	8.402%	$40.0871	$40.09	$40.10	$40.10
Purchase #6	$38.60	3.363%	$39.8981	$39.90	$39.90	$39.90
Purchase #7	$29.75	13.710%	$33.8287	$33.83	$33.85	$33.80
7 purchase totals =	$480.32		$533.0801	$533.09	$533.15	$533.10