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	$111.66	6.169%	$118.5483	$118.55	$118.55	$118.50
Purchase #2	$118.32	8.467%	$128.3382	$128.34	$128.35	$128.30
Purchase #3	$142.60	5.440%	$150.3574	$150.36	$150.35	$150.40
Purchase #4	$73.72	12.221%	$82.7293	$82.73	$82.75	$82.70
Purchase #5	$80.34	6.554%	$85.6055	$85.61	$85.60	$85.60
Purchase #6	$210.73	3.587%	$218.2889	$218.29	$218.30	$218.30
Purchase #7	$139.63	4.579%	$146.0237	$146.02	$146.00	$146.00
7 purchase totals =	$877.00		$929.8913	$929.90	$929.90	$929.80