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	$89.79	10.211%	$98.9585	$98.96	$98.95	$99.00
Purchase #2	$31.63	6.759%	$33.7679	$33.77	$33.75	$33.80
Purchase #3	$62.57	13.188%	$70.8217	$70.82	$70.80	$70.80
Purchase #4	$140.53	9.261%	$153.5445	$153.54	$153.55	$153.50
Purchase #5	$158.76	4.258%	$165.52	$165.52	$165.50	$165.50
Purchase #6	$166.47	3.189%	$171.7787	$171.78	$171.80	$171.80
Purchase #7	$190.38	12.567%	$214.3051	$214.31	$214.30	$214.30
7 purchase totals =	$840.13		$908.6964	$908.70	$908.65	$908.70