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	$103.91	7.133%	$111.3219	$111.32	$111.30	$111.30
Purchase #2	$218.37	3.268%	$225.5063	$225.51	$225.50	$225.50
Purchase #3	$185.73	12.535%	$209.0113	$209.01	$209.00	$209.00
Purchase #4	$205.52	10.676%	$227.4613	$227.46	$227.45	$227.50
Purchase #5	$117.91	7.500%	$126.7533	$126.75	$126.75	$126.80
Purchase #6	$141.92	9.696%	$155.6806	$155.68	$155.70	$155.70
Purchase #7	$130.25	3.581%	$134.9143	$134.91	$134.90	$134.90
7 purchase totals =	$1,103.61		$1,190.6490	$1,190.64	$1,190.60	$1,190.70