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	$136.49	6.543%	$145.4205	$145.42	$145.40	$145.40
Purchase #2	$39.73	5.853%	$42.0554	$42.06	$42.05	$42.10
Purchase #3	$82.46	4.503%	$86.1732	$86.17	$86.15	$86.20
Purchase #4	$87.57	13.809%	$99.6625	$99.66	$99.65	$99.70
Purchase #5	$31.61	10.192%	$34.8317	$34.83	$34.85	$34.80
Purchase #6	$104.25	9.826%	$114.4936	$114.49	$114.50	$114.50
Purchase #7	$159.89	3.652%	$165.7292	$165.73	$165.75	$165.70
7 purchase totals =	$642.00		$688.3661	$688.36	$688.35	$688.40