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	$166.85	6.527%	$177.7403	$177.74	$177.75	$177.70
Purchase #2	$128.94	10.733%	$142.7791	$142.78	$142.80	$142.80
Purchase #3	$151.41	13.161%	$171.3371	$171.34	$171.35	$171.30
Purchase #4	$140.91	4.688%	$147.5159	$147.52	$147.50	$147.50
Purchase #5	$112.92	9.385%	$123.5175	$123.52	$123.50	$123.50
Purchase #6	$65.39	7.578%	$70.3453	$70.35	$70.35	$70.30
Purchase #7	$82.61	13.143%	$93.4674	$93.47	$93.45	$93.50
7 purchase totals =	$849.03		$926.7026	$926.72	$926.70	$926.60