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	$83.77	7.720%	$90.237	$90.24	$90.25	$90.20
Purchase #2	$116.69	12.604%	$131.3976	$131.40	$131.40	$131.40
Purchase #3	$41.89	13.456%	$47.5267	$47.53	$47.55	$47.50
Purchase #4	$219.55	9.862%	$241.202	$241.20	$241.20	$241.20
Purchase #5	$171.69	6.576%	$182.9803	$182.98	$183.00	$183.00
Purchase #6	$104.98	4.518%	$109.723	$109.72	$109.70	$109.70
Purchase #7	$21.98	10.750%	$24.3429	$24.34	$24.35	$24.30
7 purchase totals =	$760.55		$827.4095	$827.41	$827.45	$827.30