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	$41.98	9.126%	$45.8111	$45.81	$45.80	$45.80
Purchase #2	$77.30	3.768%	$80.2127	$80.21	$80.20	$80.20
Purchase #3	$25.84	6.725%	$27.5777	$27.58	$27.60	$27.60
Purchase #4	$57.84	4.494%	$60.4393	$60.44	$60.45	$60.40
Purchase #5	$194.64	4.844%	$204.0684	$204.07	$204.05	$204.10
Purchase #6	$33.59	11.353%	$37.4035	$37.40	$37.40	$37.40
Purchase #7	$79.89	13.665%	$90.807	$90.81	$90.80	$90.80
7 purchase totals =	$511.08		$546.3197	$546.32	$546.30	$546.30