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	$154.46	6.436%	$164.401	$164.40	$164.40	$164.40
Purchase #2	$69.94	12.306%	$78.5468	$78.55	$78.55	$78.50
Purchase #3	$51.80	12.730%	$58.3941	$58.39	$58.40	$58.40
Purchase #4	$145.32	4.341%	$151.6283	$151.63	$151.65	$151.60
Purchase #5	$17.76	4.275%	$18.5192	$18.52	$18.50	$18.50
Purchase #6	$104.40	4.213%	$108.7984	$108.80	$108.80	$108.80
Purchase #7	$133.83	5.398%	$141.0541	$141.05	$141.05	$141.10
7 purchase totals =	$677.51		$721.3419	$721.34	$721.35	$721.30