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	$166.46	11.220%	$185.1368	$185.14	$185.15	$185.10
Purchase #2	$102.77	5.578%	$108.5025	$108.50	$108.50	$108.50
Purchase #3	$154.91	5.536%	$163.4858	$163.49	$163.50	$163.50
Purchase #4	$64.32	4.822%	$67.4215	$67.42	$67.40	$67.40
Purchase #5	$123.81	12.689%	$139.5203	$139.52	$139.50	$139.50
Purchase #6	$81.32	8.667%	$88.368	$88.37	$88.35	$88.40
Purchase #7	$166.70	12.446%	$187.4475	$187.45	$187.45	$187.40
7 purchase totals =	$860.29		$939.8824	$939.89	$939.85	$939.80