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	$59.95	10.160%	$66.0409	$66.04	$66.05	$66.00
Purchase #2	$153.33	10.541%	$169.4925	$169.49	$169.50	$169.50
Purchase #3	$35.94	12.116%	$40.2945	$40.29	$40.30	$40.30
Purchase #4	$50.55	4.577%	$52.8637	$52.86	$52.85	$52.90
Purchase #5	$231.46	9.547%	$253.5575	$253.56	$253.55	$253.60
Purchase #6	$30.94	4.261%	$32.2584	$32.26	$32.25	$32.30
Purchase #7	$237.72	9.219%	$259.6354	$259.64	$259.65	$259.60
7 purchase totals =	$799.89		$874.1429	$874.14	$874.15	$874.20