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	$29.91	3.769%	$31.0373	$31.04	$31.05	$31.00
Purchase #2	$20.83	5.221%	$21.9175	$21.92	$21.90	$21.90
Purchase #3	$79.89	4.786%	$83.7135	$83.71	$83.70	$83.70
Purchase #4	$30.69	12.417%	$34.5008	$34.50	$34.50	$34.50
Purchase #5	$29.68	10.800%	$32.8854	$32.89	$32.90	$32.90
Purchase #6	$43.62	11.477%	$48.6263	$48.63	$48.65	$48.60
Purchase #7	$26.84	5.218%	$28.2405	$28.24	$28.25	$28.20
7 purchase totals =	$261.46		$280.9213	$280.93	$280.95	$280.80