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	$98.35	9.306%	$107.5025	$107.50	$107.50	$107.50
Purchase #2	$89.39	12.174%	$100.2723	$100.27	$100.25	$100.30
Purchase #3	$11.32	10.865%	$12.5499	$12.55	$12.55	$12.50
Purchase #4	$128.93	10.121%	$141.979	$141.98	$142.00	$142.00
Purchase #5	$135.28	13.570%	$153.6375	$153.64	$153.65	$153.60
Purchase #6	$193.61	12.110%	$217.0562	$217.06	$217.05	$217.10
Purchase #7	$35.43	8.767%	$38.5361	$38.54	$38.55	$38.50
7 purchase totals =	$692.31		$771.5335	$771.54	$771.55	$771.50