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	$102.42	8.741%	$111.3725	$111.37	$111.35	$111.40
Purchase #2	$159.76	4.421%	$166.823	$166.82	$166.80	$166.80
Purchase #3	$180.56	3.233%	$186.3975	$186.40	$186.40	$186.40
Purchase #4	$13.95	11.347%	$15.5329	$15.53	$15.55	$15.50
Purchase #5	$222.90	6.651%	$237.7251	$237.73	$237.75	$237.70
Purchase #6	$48.31	7.770%	$52.0637	$52.06	$52.05	$52.10
Purchase #7	$98.85	11.156%	$109.8777	$109.88	$109.90	$109.90
7 purchase totals =	$826.75		$879.7924	$879.79	$879.80	$879.80