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	$56.39	3.587%	$58.4127	$58.41	$58.40	$58.40
Purchase #2	$153.76	7.563%	$165.3889	$165.39	$165.40	$165.40
Purchase #3	$82.31	8.366%	$89.1961	$89.20	$89.20	$89.20
Purchase #4	$39.56	8.777%	$43.0322	$43.03	$43.05	$43.00
Purchase #5	$72.94	12.200%	$81.8387	$81.84	$81.85	$81.80
Purchase #6	$230.88	13.689%	$262.4852	$262.49	$262.50	$262.50
Purchase #7	$19.38	10.820%	$21.4769	$21.48	$21.50	$21.50
7 purchase totals =	$655.22		$721.8307	$721.84	$721.90	$721.80