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	$123.25	10.765%	$136.5179	$136.52	$136.50	$136.50
Purchase #2	$53.65	13.377%	$60.8268	$60.83	$60.85	$60.80
Purchase #3	$168.93	11.742%	$188.7658	$188.77	$188.75	$188.80
Purchase #4	$67.88	4.231%	$70.752	$70.75	$70.75	$70.80
Purchase #5	$246.52	9.329%	$269.5179	$269.52	$269.50	$269.50
Purchase #6	$194.70	12.409%	$218.8603	$218.86	$218.85	$218.90
Purchase #7	$100.52	9.198%	$109.7658	$109.77	$109.75	$109.80
7 purchase totals =	$955.45		$1,055.0065	$1,055.02	$1,054.95	$1,055.10