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	$167.76	12.372%	$188.5153	$188.52	$188.50	$188.50
Purchase #2	$229.65	5.599%	$242.5081	$242.51	$242.50	$242.50
Purchase #3	$27.60	3.626%	$28.6008	$28.60	$28.60	$28.60
Purchase #4	$231.91	3.705%	$240.5023	$240.50	$240.50	$240.50
Purchase #5	$29.68	4.750%	$31.0898	$31.09	$31.10	$31.10
Purchase #6	$128.83	8.589%	$139.8952	$139.90	$139.90	$139.90
Purchase #7	$206.96	12.249%	$232.3105	$232.31	$232.30	$232.30
7 purchase totals =	$1,022.39		$1,103.4220	$1,103.43	$1,103.40	$1,103.40