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	$244.49	11.754%	$273.2274	$273.23	$273.25	$273.20
Purchase #2	$77.85	9.576%	$85.3049	$85.30	$85.30	$85.30
Purchase #3	$250.56	11.786%	$280.091	$280.09	$280.10	$280.10
Purchase #4	$248.88	6.397%	$264.8009	$264.80	$264.80	$264.80
Purchase #5	$104.75	3.861%	$108.7944	$108.79	$108.80	$108.80
Purchase #6	$74.57	11.678%	$83.2783	$83.28	$83.30	$83.30
Purchase #7	$174.72	12.509%	$196.5757	$196.58	$196.60	$196.60
7 purchase totals =	$1,175.82		$1,292.0726	$1,292.07	$1,292.15	$1,292.10