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	$81.99	10.713%	$90.7736	$90.77	$90.75	$90.80
Purchase #2	$151.37	9.172%	$165.2537	$165.25	$165.25	$165.30
Purchase #3	$101.51	7.765%	$109.3923	$109.39	$109.40	$109.40
Purchase #4	$203.77	5.857%	$215.7048	$215.70	$215.70	$215.70
Purchase #5	$168.92	11.228%	$187.8863	$187.89	$187.90	$187.90
Purchase #6	$74.52	9.247%	$81.4109	$81.41	$81.40	$81.40
Purchase #7	$117.73	4.830%	$123.4164	$123.42	$123.40	$123.40
7 purchase totals =	$899.81		$973.8380	$973.83	$973.80	$973.90