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	$126.75	13.873%	$144.334	$144.33	$144.35	$144.30
Purchase #2	$51.31	6.412%	$54.6	$54.60	$54.60	$54.60
Purchase #3	$19.98	9.656%	$21.9093	$21.91	$21.90	$21.90
Purchase #4	$5.44	8.121%	$5.8818	$5.88	$5.90	$5.90
Purchase #5	$118.43	12.337%	$133.0407	$133.04	$133.05	$133.00
Purchase #6	$101.97	7.113%	$109.2231	$109.22	$109.20	$109.20
Purchase #7	$180.92	5.528%	$190.9213	$190.92	$190.90	$190.90
7 purchase totals =	$604.80		$659.9102	$659.90	$659.90	$659.80