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	$36.99	3.334%	$38.2232	$38.22	$38.20	$38.20
Purchase #2	$164.84	6.483%	$175.5266	$175.53	$175.55	$175.50
Purchase #3	$181.53	5.122%	$190.828	$190.83	$190.85	$190.80
Purchase #4	$154.69	6.807%	$165.2197	$165.22	$165.20	$165.20
Purchase #5	$130.42	7.166%	$139.7659	$139.77	$139.75	$139.80
Purchase #6	$108.80	9.341%	$118.963	$118.96	$118.95	$119.00
Purchase #7	$59.27	4.379%	$61.8654	$61.87	$61.85	$61.90
7 purchase totals =	$836.54		$890.3918	$890.40	$890.35	$890.40