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	$154.68	6.500%	$164.7342	$164.73	$164.75	$164.70
Purchase #2	$37.85	12.452%	$42.5631	$42.56	$42.55	$42.60
Purchase #3	$234.95	11.127%	$261.0929	$261.09	$261.10	$261.10
Purchase #4	$190.79	13.641%	$216.8157	$216.82	$216.80	$216.80
Purchase #5	$69.77	12.654%	$78.5987	$78.60	$78.60	$78.60
Purchase #6	$174.69	7.530%	$187.8442	$187.84	$187.85	$187.80
Purchase #7	$109.99	4.253%	$114.6679	$114.67	$114.65	$114.70
7 purchase totals =	$972.72		$1,066.3167	$1,066.31	$1,066.30	$1,066.30