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	$152.70	4.139%	$159.0203	$159.02	$159.00	$159.00
Purchase #2	$218.50	11.392%	$243.3915	$243.39	$243.40	$243.40
Purchase #3	$93.73	9.374%	$102.5163	$102.52	$102.50	$102.50
Purchase #4	$12.45	5.476%	$13.1318	$13.13	$13.15	$13.10
Purchase #5	$50.76	8.692%	$55.1721	$55.17	$55.15	$55.20
Purchase #6	$70.37	11.219%	$78.2648	$78.26	$78.25	$78.30
Purchase #7	$176.46	7.192%	$189.151	$189.15	$189.15	$189.20
7 purchase totals =	$774.97		$840.6478	$840.64	$840.60	$840.70