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	$37.73	13.662%	$42.8847	$42.88	$42.90	$42.90
Purchase #2	$243.56	10.603%	$269.3847	$269.38	$269.40	$269.40
Purchase #3	$238.94	7.364%	$256.5355	$256.54	$256.55	$256.50
Purchase #4	$160.78	6.617%	$171.4188	$171.42	$171.40	$171.40
Purchase #5	$238.65	8.562%	$259.0832	$259.08	$259.10	$259.10
Purchase #6	$83.38	10.835%	$92.4142	$92.41	$92.40	$92.40
Purchase #7	$171.81	8.364%	$186.1802	$186.18	$186.20	$186.20
7 purchase totals =	$1,174.85		$1,277.9013	$1,277.89	$1,277.95	$1,277.90