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	$108.34	3.258%	$111.8697	$111.87	$111.85	$111.90
Purchase #2	$243.75	6.290%	$259.0819	$259.08	$259.10	$259.10
Purchase #3	$178.84	4.444%	$186.7876	$186.79	$186.80	$186.80
Purchase #4	$208.26	12.518%	$234.33	$234.33	$234.35	$234.30
Purchase #5	$91.43	7.449%	$98.2406	$98.24	$98.25	$98.20
Purchase #6	$151.50	13.546%	$172.0222	$172.02	$172.00	$172.00
Purchase #7	$32.64	6.801%	$34.8598	$34.86	$34.85	$34.90
7 purchase totals =	$1,014.76		$1,097.1918	$1,097.19	$1,097.20	$1,097.20