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	$55.42	9.798%	$60.8501	$60.85	$60.85	$60.90
Purchase #2	$43.56	4.739%	$45.6243	$45.62	$45.60	$45.60
Purchase #3	$83.62	10.151%	$92.1083	$92.11	$92.10	$92.10
Purchase #4	$88.60	7.243%	$95.0173	$95.02	$95.00	$95.00
Purchase #5	$12.93	6.576%	$13.7803	$13.78	$13.80	$13.80
Purchase #6	$87.61	9.136%	$95.614	$95.61	$95.60	$95.60
Purchase #7	$160.46	4.276%	$167.3213	$167.32	$167.30	$167.30
7 purchase totals =	$532.20		$570.3156	$570.31	$570.25	$570.30