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	$90.45	10.384%	$99.8423	$99.84	$99.85	$99.80
Purchase #2	$111.65	10.665%	$123.5575	$123.56	$123.55	$123.60
Purchase #3	$203.96	3.296%	$210.6825	$210.68	$210.70	$210.70
Purchase #4	$77.67	8.722%	$84.4444	$84.44	$84.45	$84.40
Purchase #5	$189.43	3.703%	$196.4446	$196.44	$196.45	$196.40
Purchase #6	$169.72	8.273%	$183.7609	$183.76	$183.75	$183.80
Purchase #7	$29.42	5.731%	$31.1061	$31.11	$31.10	$31.10
7 purchase totals =	$872.30		$929.8383	$929.83	$929.85	$929.80