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	$83.53	4.748%	$87.496	$87.50	$87.50	$87.50
Purchase #2	$215.66	9.775%	$236.7408	$236.74	$236.75	$236.70
Purchase #3	$85.60	5.409%	$90.2301	$90.23	$90.25	$90.20
Purchase #4	$86.89	5.129%	$91.3466	$91.35	$91.35	$91.30
Purchase #5	$99.91	8.513%	$108.4153	$108.42	$108.40	$108.40
Purchase #6	$156.54	6.689%	$167.011	$167.01	$167.00	$167.00
Purchase #7	$123.43	13.142%	$139.6512	$139.65	$139.65	$139.70
7 purchase totals =	$851.56		$920.8910	$920.90	$920.90	$920.80