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	$45.28	7.192%	$48.5365	$48.54	$48.55	$48.50
Purchase #2	$144.60	4.332%	$150.8641	$150.86	$150.85	$150.90
Purchase #3	$247.28	13.598%	$280.9051	$280.91	$280.90	$280.90
Purchase #4	$79.45	12.528%	$89.4035	$89.40	$89.40	$89.40
Purchase #5	$70.45	7.503%	$75.7359	$75.74	$75.75	$75.70
Purchase #6	$95.95	12.148%	$107.606	$107.61	$107.60	$107.60
Purchase #7	$91.93	9.789%	$100.929	$100.93	$100.95	$100.90
7 purchase totals =	$774.94		$853.9801	$853.99	$854.00	$853.90