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	$108.46	7.495%	$116.5891	$116.59	$116.60	$116.60
Purchase #2	$128.37	9.285%	$140.2892	$140.29	$140.30	$140.30
Purchase #3	$206.65	7.456%	$222.0578	$222.06	$222.05	$222.10
Purchase #4	$116.44	9.849%	$127.9082	$127.91	$127.90	$127.90
Purchase #5	$135.30	3.252%	$139.7	$139.70	$139.70	$139.70
Purchase #6	$76.49	9.365%	$83.6533	$83.65	$83.65	$83.70
Purchase #7	$115.91	6.663%	$123.6331	$123.63	$123.65	$123.60
7 purchase totals =	$887.62		$953.8307	$953.83	$953.85	$953.90