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	$179.45	5.583%	$189.4687	$189.47	$189.45	$189.50
Purchase #2	$39.81	8.767%	$43.3001	$43.30	$43.30	$43.30
Purchase #3	$168.59	12.338%	$189.3906	$189.39	$189.40	$189.40
Purchase #4	$61.32	5.213%	$64.5166	$64.52	$64.50	$64.50
Purchase #5	$184.90	8.630%	$200.8569	$200.86	$200.85	$200.90
Purchase #6	$222.77	13.815%	$253.5457	$253.55	$253.55	$253.50
Purchase #7	$159.25	10.698%	$176.2866	$176.29	$176.30	$176.30
7 purchase totals =	$1,016.09		$1,117.3652	$1,117.38	$1,117.35	$1,117.40