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	$53.82	10.514%	$59.4786	$59.48	$59.50	$59.50
Purchase #2	$55.25	8.703%	$60.0584	$60.06	$60.05	$60.10
Purchase #3	$27.76	5.864%	$29.3878	$29.39	$29.40	$29.40
Purchase #4	$95.65	10.169%	$105.3766	$105.38	$105.40	$105.40
Purchase #5	$171.27	7.355%	$183.8669	$183.87	$183.85	$183.90
Purchase #6	$185.97	12.330%	$208.9001	$208.90	$208.90	$208.90
Purchase #7	$188.61	12.437%	$212.0674	$212.07	$212.05	$212.10
7 purchase totals =	$778.33		$859.1358	$859.15	$859.15	$859.30