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	$144.33	13.689%	$164.0873	$164.09	$164.10	$164.10
Purchase #2	$40.87	3.363%	$42.2445	$42.24	$42.25	$42.20
Purchase #3	$96.32	6.255%	$102.3448	$102.34	$102.35	$102.30
Purchase #4	$52.96	9.226%	$57.8461	$57.85	$57.85	$57.80
Purchase #5	$199.81	11.464%	$222.7162	$222.72	$222.70	$222.70
Purchase #6	$35.47	9.184%	$38.7276	$38.73	$38.75	$38.70
Purchase #7	$59.97	12.185%	$67.2773	$67.28	$67.30	$67.30
7 purchase totals =	$629.73		$695.2438	$695.25	$695.30	$695.10