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	$70.59	10.842%	$78.2434	$78.24	$78.25	$78.20
Purchase #2	$94.96	7.234%	$101.8294	$101.83	$101.85	$101.80
Purchase #3	$48.61	3.515%	$50.3186	$50.32	$50.30	$50.30
Purchase #4	$42.69	9.201%	$46.6179	$46.62	$46.60	$46.60
Purchase #5	$57.54	3.389%	$59.49	$59.49	$59.50	$59.50
Purchase #6	$29.87	4.397%	$31.1834	$31.18	$31.20	$31.20
Purchase #7	$186.46	10.527%	$206.0886	$206.09	$206.10	$206.10
7 purchase totals =	$530.72		$573.7713	$573.77	$573.80	$573.70