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	$87.56	3.865%	$90.9442	$90.94	$90.95	$90.90
Purchase #2	$86.72	12.695%	$97.7291	$97.73	$97.75	$97.70
Purchase #3	$38.53	3.571%	$39.9059	$39.91	$39.90	$39.90
Purchase #4	$109.25	12.796%	$123.2296	$123.23	$123.25	$123.20
Purchase #5	$244.30	11.466%	$272.3114	$272.31	$272.30	$272.30
Purchase #6	$141.74	5.868%	$150.0573	$150.06	$150.05	$150.10
Purchase #7	$140.99	13.288%	$159.7248	$159.72	$159.70	$159.70
7 purchase totals =	$849.09		$933.9023	$933.90	$933.90	$933.80