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	$245.81	6.349%	$261.4165	$261.42	$261.40	$261.40
Purchase #2	$108.95	5.127%	$114.5359	$114.54	$114.55	$114.50
Purchase #3	$213.27	12.342%	$239.5918	$239.59	$239.60	$239.60
Purchase #4	$71.98	12.337%	$80.8602	$80.86	$80.85	$80.90
Purchase #5	$153.54	13.487%	$174.2479	$174.25	$174.25	$174.20
Purchase #6	$145.48	4.704%	$152.3234	$152.32	$152.30	$152.30
Purchase #7	$201.25	5.287%	$211.8901	$211.89	$211.90	$211.90
7 purchase totals =	$1,140.28		$1,234.8658	$1,234.87	$1,234.85	$1,234.80