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	$158.39	10.123%	$174.4238	$174.42	$174.40	$174.40
Purchase #2	$236.94	5.449%	$249.8509	$249.85	$249.85	$249.90
Purchase #3	$12.46	7.634%	$13.4112	$13.41	$13.40	$13.40
Purchase #4	$115.86	5.341%	$122.0481	$122.05	$122.05	$122.00
Purchase #5	$27.69	13.217%	$31.3498	$31.35	$31.35	$31.30
Purchase #6	$153.89	11.170%	$171.0795	$171.08	$171.10	$171.10
Purchase #7	$57.64	3.102%	$59.428	$59.43	$59.45	$59.40
7 purchase totals =	$762.87		$821.5913	$821.59	$821.60	$821.50