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	$82.36	3.590%	$85.3167	$85.32	$85.30	$85.30
Purchase #2	$146.44	4.231%	$152.6359	$152.64	$152.65	$152.60
Purchase #3	$33.68	4.708%	$35.2657	$35.27	$35.25	$35.30
Purchase #4	$47.99	12.457%	$53.9681	$53.97	$53.95	$54.00
Purchase #5	$6.48	13.714%	$7.3687	$7.37	$7.35	$7.40
Purchase #6	$132.40	7.396%	$142.1923	$142.19	$142.20	$142.20
Purchase #7	$97.25	6.456%	$103.5285	$103.53	$103.55	$103.50
7 purchase totals =	$546.60		$580.2759	$580.29	$580.25	$580.30