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	$109.54	3.308%	$113.1636	$113.16	$113.15	$113.20
Purchase #2	$240.49	12.294%	$270.0558	$270.06	$270.05	$270.10
Purchase #3	$93.77	6.573%	$99.9335	$99.93	$99.95	$99.90
Purchase #4	$153.33	4.451%	$160.1547	$160.15	$160.15	$160.20
Purchase #5	$110.64	9.849%	$121.5369	$121.54	$121.55	$121.50
Purchase #6	$139.52	4.257%	$145.4594	$145.46	$145.45	$145.50
Purchase #7	$73.32	7.583%	$78.8799	$78.88	$78.90	$78.90
7 purchase totals =	$920.61		$989.1838	$989.18	$989.20	$989.30