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	$96.89	3.352%	$100.1378	$100.14	$100.15	$100.10
Purchase #2	$85.59	7.723%	$92.2001	$92.20	$92.20	$92.20
Purchase #3	$112.43	5.384%	$118.4832	$118.48	$118.50	$118.50
Purchase #4	$29.61	3.840%	$30.747	$30.75	$30.75	$30.70
Purchase #5	$64.82	12.256%	$72.7643	$72.76	$72.75	$72.80
Purchase #6	$198.25	8.511%	$215.1231	$215.12	$215.10	$215.10
Purchase #7	$57.85	13.561%	$65.695	$65.70	$65.70	$65.70
7 purchase totals =	$645.44		$695.1505	$695.15	$695.15	$695.10