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	$166.43	12.720%	$187.5999	$187.60	$187.60	$187.60
Purchase #2	$50.85	6.497%	$54.1537	$54.15	$54.15	$54.20
Purchase #3	$114.48	10.314%	$126.2875	$126.29	$126.30	$126.30
Purchase #4	$84.48	6.346%	$89.8411	$89.84	$89.85	$89.80
Purchase #5	$132.51	13.645%	$150.591	$150.59	$150.60	$150.60
Purchase #6	$148.58	13.783%	$169.0588	$169.06	$169.05	$169.10
Purchase #7	$139.74	6.436%	$148.7337	$148.73	$148.75	$148.70
7 purchase totals =	$837.07		$926.2657	$926.26	$926.30	$926.30