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	$45.67	10.313%	$50.3799	$50.38	$50.40	$50.40
Purchase #2	$33.83	11.632%	$37.7651	$37.77	$37.75	$37.80
Purchase #3	$176.30	7.582%	$189.6671	$189.67	$189.65	$189.70
Purchase #4	$229.60	5.195%	$241.5277	$241.53	$241.55	$241.50
Purchase #5	$123.73	12.574%	$139.2878	$139.29	$139.30	$139.30
Purchase #6	$248.59	6.426%	$264.5644	$264.56	$264.55	$264.60
Purchase #7	$5.95	3.108%	$6.1349	$6.13	$6.15	$6.10
7 purchase totals =	$863.67		$929.3269	$929.33	$929.35	$929.40