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	$206.77	12.144%	$231.8801	$231.88	$231.90	$231.90
Purchase #2	$160.58	10.781%	$177.8921	$177.89	$177.90	$177.90
Purchase #3	$78.37	5.611%	$82.7673	$82.77	$82.75	$82.80
Purchase #4	$46.54	4.778%	$48.7637	$48.76	$48.75	$48.80
Purchase #5	$231.86	7.319%	$248.8298	$248.83	$248.85	$248.80
Purchase #6	$247.58	3.121%	$255.307	$255.31	$255.30	$255.30
Purchase #7	$141.55	3.732%	$146.8326	$146.83	$146.85	$146.80
7 purchase totals =	$1,113.25		$1,192.2726	$1,192.27	$1,192.30	$1,192.30