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	$74.80	3.866%	$77.6918	$77.69	$77.70	$77.70
Purchase #2	$210.96	10.871%	$233.8935	$233.89	$233.90	$233.90
Purchase #3	$128.82	12.170%	$144.4974	$144.50	$144.50	$144.50
Purchase #4	$214.89	5.456%	$226.6144	$226.61	$226.60	$226.60
Purchase #5	$73.49	9.506%	$80.476	$80.48	$80.50	$80.50
Purchase #6	$94.90	7.340%	$101.8657	$101.87	$101.85	$101.90
Purchase #7	$141.69	10.526%	$156.6043	$156.60	$156.60	$156.60
7 purchase totals =	$939.55		$1,021.6431	$1,021.64	$1,021.65	$1,021.70