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	$55.82	5.158%	$58.6992	$58.70	$58.70	$58.70
Purchase #2	$137.63	3.619%	$142.6108	$142.61	$142.60	$142.60
Purchase #3	$10.53	9.863%	$11.5686	$11.57	$11.55	$11.60
Purchase #4	$19.59	3.447%	$20.2653	$20.27	$20.25	$20.30
Purchase #5	$135.67	9.119%	$148.0417	$148.04	$148.05	$148.00
Purchase #6	$144.37	12.834%	$162.8984	$162.90	$162.90	$162.90
Purchase #7	$179.75	5.759%	$190.1018	$190.10	$190.10	$190.10
7 purchase totals =	$683.36		$734.1858	$734.19	$734.15	$734.20