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	$114.85	12.709%	$129.4463	$129.45	$129.45	$129.40
Purchase #2	$100.90	6.357%	$107.3142	$107.31	$107.30	$107.30
Purchase #3	$79.55	12.772%	$89.7101	$89.71	$89.70	$89.70
Purchase #4	$85.64	7.344%	$91.9294	$91.93	$91.95	$91.90
Purchase #5	$79.51	8.279%	$86.0926	$86.09	$86.10	$86.10
Purchase #6	$112.67	3.331%	$116.423	$116.42	$116.40	$116.40
Purchase #7	$40.91	3.719%	$42.4314	$42.43	$42.45	$42.40
7 purchase totals =	$614.03		$663.3470	$663.34	$663.35	$663.20