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	$24.53	12.119%	$27.5028	$27.50	$27.50	$27.50
Purchase #2	$65.88	9.528%	$72.157	$72.16	$72.15	$72.20
Purchase #3	$151.76	12.791%	$171.1716	$171.17	$171.15	$171.20
Purchase #4	$240.87	7.559%	$259.0774	$259.08	$259.10	$259.10
Purchase #5	$249.48	10.456%	$275.5656	$275.57	$275.55	$275.60
Purchase #6	$150.30	6.566%	$160.1687	$160.17	$160.15	$160.20
Purchase #7	$34.97	13.195%	$39.5843	$39.58	$39.60	$39.60
7 purchase totals =	$917.79		$1,005.2274	$1,005.23	$1,005.20	$1,005.40