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	$97.86	6.533%	$104.2532	$104.25	$104.25	$104.30
Purchase #2	$130.82	12.234%	$146.8245	$146.82	$146.80	$146.80
Purchase #3	$110.25	11.612%	$123.0522	$123.05	$123.05	$123.10
Purchase #4	$47.75	13.810%	$54.3443	$54.34	$54.35	$54.30
Purchase #5	$200.70	10.412%	$221.5969	$221.60	$221.60	$221.60
Purchase #6	$138.61	5.160%	$145.7623	$145.76	$145.75	$145.80
Purchase #7	$120.67	7.618%	$129.8626	$129.86	$129.85	$129.90
7 purchase totals =	$846.66		$925.6960	$925.68	$925.65	$925.80