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	$109.27	13.575%	$124.1034	$124.10	$124.10	$124.10
Purchase #2	$150.44	11.320%	$167.4698	$167.47	$167.45	$167.50
Purchase #3	$31.30	5.784%	$33.1104	$33.11	$33.10	$33.10
Purchase #4	$187.34	7.236%	$200.8959	$200.90	$200.90	$200.90
Purchase #5	$101.28	6.633%	$107.9979	$108.00	$108.00	$108.00
Purchase #6	$184.72	10.493%	$204.1027	$204.10	$204.10	$204.10
Purchase #7	$71.39	13.323%	$80.9013	$80.90	$80.90	$80.90
7 purchase totals =	$835.74		$918.5814	$918.58	$918.55	$918.60