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	$94.86	4.206%	$98.8498	$98.85	$98.85	$98.80
Purchase #2	$38.25	9.865%	$42.0234	$42.02	$42.00	$42.00
Purchase #3	$129.36	13.859%	$147.288	$147.29	$147.30	$147.30
Purchase #4	$187.32	13.257%	$212.153	$212.15	$212.15	$212.20
Purchase #5	$13.93	11.690%	$15.5584	$15.56	$15.55	$15.60
Purchase #6	$111.89	10.333%	$123.4516	$123.45	$123.45	$123.50
Purchase #7	$6.95	12.634%	$7.8281	$7.83	$7.85	$7.80
7 purchase totals =	$582.56		$647.1523	$647.15	$647.15	$647.20