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	$140.53	5.591%	$148.387	$148.39	$148.40	$148.40
Purchase #2	$128.61	6.137%	$136.5028	$136.50	$136.50	$136.50
Purchase #3	$98.34	4.136%	$102.4073	$102.41	$102.40	$102.40
Purchase #4	$40.39	11.176%	$44.904	$44.90	$44.90	$44.90
Purchase #5	$99.53	11.759%	$111.2337	$111.23	$111.25	$111.20
Purchase #6	$241.45	3.405%	$249.6714	$249.67	$249.65	$249.70
Purchase #7	$95.99	8.404%	$104.057	$104.06	$104.05	$104.10
7 purchase totals =	$844.84		$897.1632	$897.16	$897.15	$897.20