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	$45.89	10.144%	$50.5451	$50.55	$50.55	$50.50
Purchase #2	$44.74	6.169%	$47.5	$47.50	$47.50	$47.50
Purchase #3	$150.91	12.499%	$169.7722	$169.77	$169.75	$169.80
Purchase #4	$138.75	12.505%	$156.1007	$156.10	$156.10	$156.10
Purchase #5	$125.51	11.410%	$139.8307	$139.83	$139.85	$139.80
Purchase #6	$94.53	9.249%	$103.2731	$103.27	$103.25	$103.30
Purchase #7	$59.63	10.682%	$65.9997	$66.00	$66.00	$66.00
7 purchase totals =	$659.96		$733.0215	$733.02	$733.00	$733.00