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	$247.34	10.145%	$272.4326	$272.43	$272.45	$272.40
Purchase #2	$75.38	13.369%	$85.4576	$85.46	$85.45	$85.50
Purchase #3	$163.84	5.642%	$173.0839	$173.08	$173.10	$173.10
Purchase #4	$57.86	7.113%	$61.9756	$61.98	$62.00	$62.00
Purchase #5	$88.90	7.214%	$95.3132	$95.31	$95.30	$95.30
Purchase #6	$18.39	6.379%	$19.5631	$19.56	$19.55	$19.60
Purchase #7	$119.74	3.165%	$123.5298	$123.53	$123.55	$123.50
7 purchase totals =	$771.45		$831.3558	$831.35	$831.40	$831.40