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	$54.57	12.629%	$61.4616	$61.46	$61.45	$61.50
Purchase #2	$29.53	8.677%	$32.0923	$32.09	$32.10	$32.10
Purchase #3	$167.66	13.638%	$190.5255	$190.53	$190.55	$190.50
Purchase #4	$239.83	4.570%	$250.7902	$250.79	$250.80	$250.80
Purchase #5	$88.68	11.806%	$99.1496	$99.15	$99.15	$99.10
Purchase #6	$146.40	9.303%	$160.0196	$160.02	$160.00	$160.00
Purchase #7	$188.49	12.617%	$212.2718	$212.27	$212.25	$212.30
7 purchase totals =	$915.16		$1,006.3106	$1,006.31	$1,006.30	$1,006.30