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	$117.29	11.804%	$131.1349	$131.13	$131.15	$131.10
Purchase #2	$96.93	3.423%	$100.2479	$100.25	$100.25	$100.20
Purchase #3	$96.89	8.843%	$105.458	$105.46	$105.45	$105.50
Purchase #4	$76.73	10.330%	$84.6562	$84.66	$84.65	$84.70
Purchase #5	$144.65	9.633%	$158.5841	$158.58	$158.60	$158.60
Purchase #6	$188.67	6.441%	$200.8222	$200.82	$200.80	$200.80
Purchase #7	$125.75	8.584%	$136.5444	$136.54	$136.55	$136.50
7 purchase totals =	$846.91		$917.4477	$917.44	$917.45	$917.40