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	$39.69	13.114%	$44.8949	$44.89	$44.90	$44.90
Purchase #2	$156.43	9.823%	$171.7961	$171.80	$171.80	$171.80
Purchase #3	$73.31	13.319%	$83.0742	$83.07	$83.05	$83.10
Purchase #4	$150.52	4.326%	$157.0315	$157.03	$157.05	$157.00
Purchase #5	$101.91	7.127%	$109.1731	$109.17	$109.15	$109.20
Purchase #6	$44.84	8.829%	$48.7989	$48.80	$48.80	$48.80
Purchase #7	$50.94	4.215%	$53.0871	$53.09	$53.10	$53.10
7 purchase totals =	$617.64		$667.8558	$667.85	$667.85	$667.90