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	$166.36	3.328%	$171.8965	$171.90	$171.90	$171.90
Purchase #2	$125.50	12.223%	$140.8399	$140.84	$140.85	$140.80
Purchase #3	$117.73	4.843%	$123.4317	$123.43	$123.45	$123.40
Purchase #4	$49.53	10.806%	$54.8822	$54.88	$54.90	$54.90
Purchase #5	$34.26	5.615%	$36.1837	$36.18	$36.20	$36.20
Purchase #6	$109.54	12.186%	$122.8885	$122.89	$122.90	$122.90
Purchase #7	$93.60	5.860%	$99.085	$99.09	$99.10	$99.10
7 purchase totals =	$696.52		$749.2075	$749.21	$749.30	$749.20