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	$136.48	3.862%	$141.7509	$141.75	$141.75	$141.80
Purchase #2	$52.82	8.771%	$57.4528	$57.45	$57.45	$57.50
Purchase #3	$56.85	7.113%	$60.8937	$60.89	$60.90	$60.90
Purchase #4	$48.97	9.224%	$53.487	$53.49	$53.50	$53.50
Purchase #5	$98.72	5.827%	$104.4724	$104.47	$104.45	$104.50
Purchase #6	$174.73	12.534%	$196.6307	$196.63	$196.65	$196.60
Purchase #7	$21.81	3.112%	$22.4887	$22.49	$22.50	$22.50
7 purchase totals =	$590.38		$637.1762	$637.17	$637.20	$637.30