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	$68.47	5.727%	$72.3913	$72.39	$72.40	$72.40
Purchase #2	$182.90	12.156%	$205.1333	$205.13	$205.15	$205.10
Purchase #3	$91.53	13.745%	$104.1108	$104.11	$104.10	$104.10
Purchase #4	$80.52	11.443%	$89.7339	$89.73	$89.75	$89.70
Purchase #5	$147.33	4.220%	$153.5473	$153.55	$153.55	$153.50
Purchase #6	$11.75	12.208%	$13.1844	$13.18	$13.20	$13.20
Purchase #7	$95.57	4.246%	$99.6279	$99.63	$99.65	$99.60
7 purchase totals =	$678.07		$737.7289	$737.72	$737.80	$737.60