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	$87.89	13.616%	$99.8571	$99.86	$99.85	$99.90
Purchase #2	$56.30	3.835%	$58.4591	$58.46	$58.45	$58.50
Purchase #3	$105.97	3.219%	$109.3812	$109.38	$109.40	$109.40
Purchase #4	$138.42	5.310%	$145.7701	$145.77	$145.75	$145.80
Purchase #5	$178.36	12.596%	$200.8262	$200.83	$200.85	$200.80
Purchase #6	$57.76	12.345%	$64.8905	$64.89	$64.90	$64.90
Purchase #7	$215.66	10.445%	$238.1857	$238.19	$238.20	$238.20
7 purchase totals =	$840.36		$917.3699	$917.38	$917.40	$917.50