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	$144.76	6.755%	$154.5385	$154.54	$154.55	$154.50
Purchase #2	$124.60	12.711%	$140.4379	$140.44	$140.45	$140.40
Purchase #3	$159.45	5.334%	$167.9551	$167.96	$167.95	$168.00
Purchase #4	$154.61	3.711%	$160.3476	$160.35	$160.35	$160.30
Purchase #5	$102.46	10.815%	$113.541	$113.54	$113.55	$113.50
Purchase #6	$54.40	13.175%	$61.5672	$61.57	$61.55	$61.60
Purchase #7	$184.49	3.397%	$190.7571	$190.76	$190.75	$190.80
7 purchase totals =	$924.77		$989.1444	$989.16	$989.15	$989.10