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	$6.98	13.121%	$7.8958	$7.90	$7.90	$7.90
Purchase #2	$125.41	10.221%	$138.2282	$138.23	$138.25	$138.20
Purchase #3	$100.61	10.873%	$111.5493	$111.55	$111.55	$111.50
Purchase #4	$59.66	4.768%	$62.5046	$62.50	$62.50	$62.50
Purchase #5	$31.81	13.340%	$36.0535	$36.05	$36.05	$36.10
Purchase #6	$179.41	4.171%	$186.8932	$186.89	$186.90	$186.90
Purchase #7	$153.66	6.249%	$163.2622	$163.26	$163.25	$163.30
7 purchase totals =	$657.54		$706.3868	$706.38	$706.40	$706.40