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	$161.73	4.308%	$168.6973	$168.70	$168.70	$168.70
Purchase #2	$83.62	10.829%	$92.6752	$92.68	$92.70	$92.70
Purchase #3	$134.50	7.395%	$144.4463	$144.45	$144.45	$144.40
Purchase #4	$79.34	12.389%	$89.1694	$89.17	$89.15	$89.20
Purchase #5	$136.39	3.206%	$140.7627	$140.76	$140.75	$140.80
Purchase #6	$160.96	3.166%	$166.056	$166.06	$166.05	$166.10
Purchase #7	$169.96	6.777%	$181.4782	$181.48	$181.50	$181.50
7 purchase totals =	$926.50		$983.2851	$983.30	$983.30	$983.40