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	$165.88	12.849%	$187.1939	$187.19	$187.20	$187.20
Purchase #2	$103.74	10.400%	$114.529	$114.53	$114.55	$114.50
Purchase #3	$57.90	13.352%	$65.6308	$65.63	$65.65	$65.60
Purchase #4	$108.74	13.367%	$123.2753	$123.28	$123.30	$123.30
Purchase #5	$185.45	10.549%	$205.0131	$205.01	$205.00	$205.00
Purchase #6	$82.98	6.690%	$88.5314	$88.53	$88.55	$88.50
Purchase #7	$200.71	8.441%	$217.6519	$217.65	$217.65	$217.70
7 purchase totals =	$905.40		$1,001.8254	$1,001.82	$1,001.90	$1,001.80