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	$95.54	7.700%	$102.8966	$102.90	$102.90	$102.90
Purchase #2	$250.27	8.783%	$272.2512	$272.25	$272.25	$272.30
Purchase #3	$231.47	7.808%	$249.5432	$249.54	$249.55	$249.50
Purchase #4	$105.32	9.570%	$115.3991	$115.40	$115.40	$115.40
Purchase #5	$99.57	3.578%	$103.1326	$103.13	$103.15	$103.10
Purchase #6	$55.40	7.691%	$59.6608	$59.66	$59.65	$59.70
Purchase #7	$234.61	8.615%	$254.8217	$254.82	$254.80	$254.80
7 purchase totals =	$1,072.18		$1,157.7052	$1,157.70	$1,157.70	$1,157.70