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	$247.48	12.741%	$279.0114	$279.01	$279.00	$279.00
Purchase #2	$209.65	6.179%	$222.6043	$222.60	$222.60	$222.60
Purchase #3	$145.31	4.123%	$151.3011	$151.30	$151.30	$151.30
Purchase #4	$144.78	6.673%	$154.4412	$154.44	$154.45	$154.40
Purchase #5	$98.49	4.232%	$102.6581	$102.66	$102.65	$102.70
Purchase #6	$130.65	11.310%	$145.4265	$145.43	$145.45	$145.40
Purchase #7	$120.45	3.688%	$124.8922	$124.89	$124.90	$124.90
7 purchase totals =	$1,096.81		$1,180.3348	$1,180.33	$1,180.35	$1,180.30