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	$68.30	4.102%	$71.1017	$71.10	$71.10	$71.10
Purchase #2	$222.32	3.838%	$230.8526	$230.85	$230.85	$230.90
Purchase #3	$109.78	9.161%	$119.8369	$119.84	$119.85	$119.80
Purchase #4	$98.72	13.601%	$112.1469	$112.15	$112.15	$112.10
Purchase #5	$240.88	12.265%	$270.4239	$270.42	$270.40	$270.40
Purchase #6	$105.97	13.607%	$120.3893	$120.39	$120.40	$120.40
Purchase #7	$10.37	11.214%	$11.5329	$11.53	$11.55	$11.50
7 purchase totals =	$856.34		$936.2842	$936.28	$936.30	$936.20