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	$85.34	4.390%	$89.0864	$89.09	$89.10	$89.10
Purchase #2	$143.31	11.819%	$160.2478	$160.25	$160.25	$160.20
Purchase #3	$16.40	12.814%	$18.5015	$18.50	$18.50	$18.50
Purchase #4	$48.57	7.581%	$52.2521	$52.25	$52.25	$52.30
Purchase #5	$81.48	13.325%	$92.3372	$92.34	$92.35	$92.30
Purchase #6	$30.97	13.387%	$35.116	$35.12	$35.10	$35.10
Purchase #7	$101.95	7.649%	$109.7482	$109.75	$109.75	$109.70
7 purchase totals =	$508.02		$557.2892	$557.30	$557.30	$557.20