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	$124.66	9.821%	$136.9029	$136.90	$136.90	$136.90
Purchase #2	$59.65	6.550%	$63.5571	$63.56	$63.55	$63.60
Purchase #3	$239.67	13.129%	$271.1363	$271.14	$271.15	$271.10
Purchase #4	$103.72	8.649%	$112.6907	$112.69	$112.70	$112.70
Purchase #5	$126.72	3.593%	$131.273	$131.27	$131.25	$131.30
Purchase #6	$162.30	6.445%	$172.7602	$172.76	$172.75	$172.80
Purchase #7	$198.38	12.142%	$222.4673	$222.47	$222.45	$222.50
7 purchase totals =	$1,015.10		$1,110.7875	$1,110.79	$1,110.75	$1,110.90