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	$89.65	13.812%	$102.0325	$102.03	$102.05	$102.00
Purchase #2	$248.29	13.130%	$280.8905	$280.89	$280.90	$280.90
Purchase #3	$27.25	4.297%	$28.4209	$28.42	$28.40	$28.40
Purchase #4	$45.26	3.395%	$46.7966	$46.80	$46.80	$46.80
Purchase #5	$6.76	12.238%	$7.5873	$7.59	$7.60	$7.60
Purchase #6	$31.76	12.246%	$35.6493	$35.65	$35.65	$35.60
Purchase #7	$135.94	7.647%	$146.3353	$146.34	$146.35	$146.30
7 purchase totals =	$584.91		$647.7124	$647.72	$647.75	$647.60