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	$97.83	7.641%	$105.3052	$105.31	$105.30	$105.30
Purchase #2	$207.77	9.539%	$227.5892	$227.59	$227.60	$227.60
Purchase #3	$237.78	9.299%	$259.8912	$259.89	$259.90	$259.90
Purchase #4	$114.32	8.114%	$123.5959	$123.60	$123.60	$123.60
Purchase #5	$241.29	3.317%	$249.2936	$249.29	$249.30	$249.30
Purchase #6	$232.85	5.637%	$245.9758	$245.98	$246.00	$246.00
Purchase #7	$101.31	9.350%	$110.7825	$110.78	$110.80	$110.80
7 purchase totals =	$1,233.15		$1,322.4334	$1,322.44	$1,322.50	$1,322.50