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	$175.91	6.591%	$187.5042	$187.50	$187.50	$187.50
Purchase #2	$138.70	5.665%	$146.5574	$146.56	$146.55	$146.60
Purchase #3	$79.49	10.820%	$88.0908	$88.09	$88.10	$88.10
Purchase #4	$96.61	13.276%	$109.4359	$109.44	$109.45	$109.40
Purchase #5	$146.87	6.821%	$156.888	$156.89	$156.90	$156.90
Purchase #6	$90.75	13.382%	$102.8942	$102.89	$102.90	$102.90
Purchase #7	$194.96	3.834%	$202.4348	$202.43	$202.45	$202.40
7 purchase totals =	$923.29		$993.8053	$993.80	$993.85	$993.80