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	$154.68	3.743%	$160.4697	$160.47	$160.45	$160.50
Purchase #2	$72.77	10.740%	$80.5855	$80.59	$80.60	$80.60
Purchase #3	$171.39	6.373%	$182.3127	$182.31	$182.30	$182.30
Purchase #4	$149.52	4.785%	$156.6745	$156.67	$156.65	$156.70
Purchase #5	$226.65	10.581%	$250.6318	$250.63	$250.65	$250.60
Purchase #6	$66.67	13.399%	$75.6031	$75.60	$75.60	$75.60
Purchase #7	$65.85	9.795%	$72.3	$72.30	$72.30	$72.30
7 purchase totals =	$907.53		$978.5773	$978.57	$978.55	$978.60