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	$172.89	4.516%	$180.6977	$180.70	$180.70	$180.70
Purchase #2	$40.56	4.610%	$42.4298	$42.43	$42.45	$42.40
Purchase #3	$246.58	5.793%	$260.8644	$260.86	$260.85	$260.90
Purchase #4	$93.58	12.845%	$105.6004	$105.60	$105.60	$105.60
Purchase #5	$154.48	9.635%	$169.3641	$169.36	$169.35	$169.40
Purchase #6	$16.92	8.566%	$18.3694	$18.37	$18.35	$18.40
Purchase #7	$72.78	11.430%	$81.0988	$81.10	$81.10	$81.10
7 purchase totals =	$797.79		$858.4246	$858.42	$858.40	$858.50