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	$31.55	5.594%	$33.3149	$33.31	$33.30	$33.30
Purchase #2	$103.70	4.178%	$108.0326	$108.03	$108.05	$108.00
Purchase #3	$99.56	13.839%	$113.3381	$113.34	$113.35	$113.30
Purchase #4	$154.69	11.329%	$172.2148	$172.21	$172.20	$172.20
Purchase #5	$166.89	7.468%	$179.3533	$179.35	$179.35	$179.40
Purchase #6	$146.71	6.526%	$156.2843	$156.28	$156.30	$156.30
Purchase #7	$32.48	9.139%	$35.4483	$35.45	$35.45	$35.40
7 purchase totals =	$735.58		$797.9863	$797.97	$798.00	$797.90