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	$35.56	4.586%	$37.1908	$37.19	$37.20	$37.20
Purchase #2	$43.72	10.313%	$48.2288	$48.23	$48.25	$48.20
Purchase #3	$117.30	8.773%	$127.5907	$127.59	$127.60	$127.60
Purchase #4	$117.96	12.765%	$133.0176	$133.02	$133.00	$133.00
Purchase #5	$127.69	5.143%	$134.2571	$134.26	$134.25	$134.30
Purchase #6	$169.40	5.645%	$178.9626	$178.96	$178.95	$179.00
Purchase #7	$247.95	13.150%	$280.5554	$280.56	$280.55	$280.60
7 purchase totals =	$859.58		$939.8030	$939.81	$939.80	$939.90