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	$83.88	8.439%	$90.9586	$90.96	$90.95	$91.00
Purchase #2	$58.56	10.681%	$64.8148	$64.81	$64.80	$64.80
Purchase #3	$130.62	10.115%	$143.8322	$143.83	$143.85	$143.80
Purchase #4	$128.42	9.189%	$140.2205	$140.22	$140.20	$140.20
Purchase #5	$145.69	13.163%	$164.8672	$164.87	$164.85	$164.90
Purchase #6	$55.88	6.686%	$59.6161	$59.62	$59.60	$59.60
Purchase #7	$150.96	8.415%	$163.6633	$163.66	$163.65	$163.70
7 purchase totals =	$754.01		$827.9727	$827.97	$827.90	$828.00