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	$76.46	6.386%	$81.3427	$81.34	$81.35	$81.30
Purchase #2	$31.69	4.290%	$33.0495	$33.05	$33.05	$33.00
Purchase #3	$248.62	9.659%	$272.6342	$272.63	$272.65	$272.60
Purchase #4	$157.58	6.783%	$168.2687	$168.27	$168.25	$168.30
Purchase #5	$79.90	3.281%	$82.5215	$82.52	$82.50	$82.50
Purchase #6	$54.35	12.420%	$61.1003	$61.10	$61.10	$61.10
Purchase #7	$187.92	11.551%	$209.6266	$209.63	$209.65	$209.60
7 purchase totals =	$836.52		$908.5435	$908.54	$908.55	$908.40