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	$47.89	11.872%	$53.5755	$53.58	$53.60	$53.60
Purchase #2	$139.62	6.642%	$148.8936	$148.89	$148.90	$148.90
Purchase #3	$70.82	3.498%	$73.2973	$73.30	$73.30	$73.30
Purchase #4	$49.83	5.528%	$52.5846	$52.58	$52.60	$52.60
Purchase #5	$70.60	11.232%	$78.5298	$78.53	$78.55	$78.50
Purchase #6	$76.65	3.626%	$79.4293	$79.43	$79.45	$79.40
Purchase #7	$120.83	4.339%	$126.0728	$126.07	$126.05	$126.10
7 purchase totals =	$576.24		$612.3829	$612.38	$612.45	$612.40