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	$114.46	12.347%	$128.5924	$128.59	$128.60	$128.60
Purchase #2	$240.78	3.855%	$250.0621	$250.06	$250.05	$250.10
Purchase #3	$225.87	7.277%	$242.3066	$242.31	$242.30	$242.30
Purchase #4	$47.96	6.728%	$51.1867	$51.19	$51.20	$51.20
Purchase #5	$171.40	11.777%	$191.5858	$191.59	$191.60	$191.60
Purchase #6	$45.78	5.818%	$48.4435	$48.44	$48.45	$48.40
Purchase #7	$159.97	11.605%	$178.5345	$178.53	$178.55	$178.50
7 purchase totals =	$1,006.22		$1,090.7116	$1,090.71	$1,090.75	$1,090.70