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	$135.61	8.237%	$146.7802	$146.78	$146.80	$146.80
Purchase #2	$154.72	3.646%	$160.3611	$160.36	$160.35	$160.40
Purchase #3	$151.43	13.661%	$172.1169	$172.12	$172.10	$172.10
Purchase #4	$27.53	13.762%	$31.3187	$31.32	$31.30	$31.30
Purchase #5	$212.71	6.218%	$225.9363	$225.94	$225.95	$225.90
Purchase #6	$162.84	7.177%	$174.527	$174.53	$174.55	$174.50
Purchase #7	$70.72	7.816%	$76.2475	$76.25	$76.25	$76.20
7 purchase totals =	$915.56		$987.2877	$987.30	$987.30	$987.20