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	$131.68	5.783%	$139.2951	$139.30	$139.30	$139.30
Purchase #2	$116.86	6.804%	$124.8112	$124.81	$124.80	$124.80
Purchase #3	$173.29	7.224%	$185.8085	$185.81	$185.80	$185.80
Purchase #4	$169.43	6.757%	$180.8784	$180.88	$180.90	$180.90
Purchase #5	$205.79	11.226%	$228.892	$228.89	$228.90	$228.90
Purchase #6	$80.88	9.257%	$88.3671	$88.37	$88.35	$88.40
Purchase #7	$142.30	13.308%	$161.2373	$161.24	$161.25	$161.20
7 purchase totals =	$1,020.23		$1,109.2896	$1,109.30	$1,109.30	$1,109.30