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	$123.32	13.193%	$139.5896	$139.59	$139.60	$139.60
Purchase #2	$19.33	5.154%	$20.3263	$20.33	$20.35	$20.30
Purchase #3	$112.55	4.189%	$117.2647	$117.26	$117.25	$117.30
Purchase #4	$195.98	6.796%	$209.2988	$209.30	$209.30	$209.30
Purchase #5	$64.78	9.449%	$70.9011	$70.90	$70.90	$70.90
Purchase #6	$198.83	6.588%	$211.9289	$211.93	$211.95	$211.90
Purchase #7	$238.89	4.191%	$248.9019	$248.90	$248.90	$248.90
7 purchase totals =	$953.68		$1,018.2113	$1,018.21	$1,018.25	$1,018.20