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	$64.37	12.817%	$72.6203	$72.62	$72.60	$72.60
Purchase #2	$60.75	7.832%	$65.5079	$65.51	$65.50	$65.50
Purchase #3	$190.80	11.276%	$212.3146	$212.31	$212.30	$212.30
Purchase #4	$200.77	10.392%	$221.634	$221.63	$221.65	$221.60
Purchase #5	$136.72	12.124%	$153.2959	$153.30	$153.30	$153.30
Purchase #6	$38.43	6.328%	$40.8619	$40.86	$40.85	$40.90
Purchase #7	$82.53	11.202%	$91.775	$91.78	$91.80	$91.80
7 purchase totals =	$774.37		$858.0096	$858.01	$858.00	$858.00