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	$35.89	7.547%	$38.5986	$38.60	$38.60	$38.60
Purchase #2	$57.46	11.827%	$64.2558	$64.26	$64.25	$64.30
Purchase #3	$127.90	13.257%	$144.8557	$144.86	$144.85	$144.90
Purchase #4	$112.41	12.345%	$126.287	$126.29	$126.30	$126.30
Purchase #5	$121.34	13.634%	$137.8835	$137.88	$137.90	$137.90
Purchase #6	$128.97	9.368%	$141.0519	$141.05	$141.05	$141.10
Purchase #7	$119.97	11.523%	$133.7941	$133.79	$133.80	$133.80
7 purchase totals =	$703.94		$786.7266	$786.73	$786.75	$786.90