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	$51.38	4.164%	$53.5195	$53.52	$53.50	$53.50
Purchase #2	$37.84	13.320%	$42.8803	$42.88	$42.90	$42.90
Purchase #3	$30.31	12.380%	$34.0624	$34.06	$34.05	$34.10
Purchase #4	$41.43	12.747%	$46.7111	$46.71	$46.70	$46.70
Purchase #5	$153.80	6.825%	$164.2969	$164.30	$164.30	$164.30
Purchase #6	$218.95	10.820%	$242.6404	$242.64	$242.65	$242.60
Purchase #7	$72.45	11.312%	$80.6455	$80.65	$80.65	$80.60
7 purchase totals =	$606.16		$664.7561	$664.76	$664.75	$664.70