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	$121.28	8.336%	$131.3899	$131.39	$131.40	$131.40
Purchase #2	$194.84	10.632%	$215.5554	$215.56	$215.55	$215.60
Purchase #3	$47.43	9.207%	$51.7969	$51.80	$51.80	$51.80
Purchase #4	$83.61	8.722%	$90.9025	$90.90	$90.90	$90.90
Purchase #5	$216.56	11.154%	$240.7151	$240.72	$240.70	$240.70
Purchase #6	$137.88	6.773%	$147.2186	$147.22	$147.20	$147.20
Purchase #7	$65.43	7.521%	$70.351	$70.35	$70.35	$70.40
7 purchase totals =	$867.03		$947.9294	$947.94	$947.90	$948.00