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	$139.79	8.144%	$151.1745	$151.17	$151.15	$151.20
Purchase #2	$32.48	6.297%	$34.5253	$34.53	$34.55	$34.50
Purchase #3	$99.63	12.192%	$111.7769	$111.78	$111.80	$111.80
Purchase #4	$138.29	12.143%	$155.0826	$155.08	$155.10	$155.10
Purchase #5	$64.37	8.443%	$69.8048	$69.80	$69.80	$69.80
Purchase #6	$80.95	5.702%	$85.5658	$85.57	$85.55	$85.60
Purchase #7	$164.74	9.228%	$179.9422	$179.94	$179.95	$179.90
7 purchase totals =	$720.25		$787.8721	$787.87	$787.90	$787.90