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	$159.55	12.741%	$179.8783	$179.88	$179.90	$179.90
Purchase #2	$59.27	10.564%	$65.5313	$65.53	$65.55	$65.50
Purchase #3	$72.83	8.397%	$78.9455	$78.95	$78.95	$78.90
Purchase #4	$86.76	6.714%	$92.5851	$92.59	$92.60	$92.60
Purchase #5	$141.83	10.575%	$156.8285	$156.83	$156.85	$156.80
Purchase #6	$229.96	12.700%	$259.1649	$259.16	$259.15	$259.20
Purchase #7	$50.51	7.109%	$54.1008	$54.10	$54.10	$54.10
7 purchase totals =	$800.71		$887.0344	$887.04	$887.10	$887.00